bluuebunny/crossref_metadata_2025 huggingface dataset:
Localization of oxalacetate keto–enol-tautomerase
Authors: Wesenberg James C. , Chaudhari Aravind , Annett Robert G.
Published: December 2009

The intracellular location of oxalacetate keto–enol-tautomerase (oxaloacetate keto–enol-isomerase) (EC 5.3.2.2) has been determined in two types of animal cells, rat liver and pig kidney. Two fractionation procedures were adopted and modified to suit each type of tissue. One fractionation procedure gave the soluble phase, microsomal and mitochondrial fractions, while the other isolated the nuclear fraction. The tautomerase is distributed among the soluble phase, microsomes and mitochondria in both tissues. Fractionation efficiency was checked by determining percentage recoveries of enzymic activity and total protein after each step, by microscopy studies and by determining the distribution of several marker enzymes.
Study of the natural antihistamine-like substance in bile of mammals
Authors: Pelletier Guy , Gauthier P. , Laflamme G. , Coan P. , Lepage M.
Published: December 2009

A natural antihistamine substance (NAS) present in bile has been investigated. It was found that the antihistamine activity was not due to proteins, lipids, pigments, or amino acids. On ion exchange chromatography and thin-layer chromatography, this activity was associated with bile acids. Many bile acids could, in varying degrees, inhibit the histamine induced guinea pig ileum contraction, desoxycholic acid being the most potent. However NAS activity could be separated from bile acids and their conjugates using a different solvent system. Furthermore, NAS showed a higher antihistamine activity than bile acids. This substance seems to be responsible for 15–20% of the activity of whole bile. The substance has not yet been identified.
Some molecular properties of rat-liver lysosomal β-glucuronidase isoenzymes
Authors: Potier M. , Gianetto R.
Published: December 2009

The isoenzymes of rat-liver lysosomal β-glucuronidase (β-D-glucuronide glucuronosohydrolase (EC 3.2.1.31)) were inactivated at different rates at 0 °C in 3 M guanidinium chloride solutions adjusted to pH 5.0. In 4 M urea buffered by 0.01 M glycylglycine, pH 7.0, isoenzymes I, III, and V were reversibly inhibited 80%. Sodium dodecyl sulfate (SDS), 0.1% in 0.01 M phosphate buffer, pH 7.0, irreversibly inhibited at 37 °C all five isoenzymes. Sedimentation analysis showed that loss of catalytic activity in these denaturing media is accompanied by dissociation into slower sedimenting subunits. SDS gel electrophoresis revealed that the isoenzymes are apparently tetramers made up of different proportions of subunits α, β, and γ having apparent molecular weights of 62 900,60 200, and 58 700, respectively. The three subunits appear to be glycoproteins.
Studies of the metabolism of asialotransferrins: nonspecific changes in the metabolic behaviour of human asialotransferrin in avians
Authors: Hatton M. W. C. , Regoeczi E.
Published: December 2009

In a previous study (Regoeczi, E. &Hatton, M. W. C. (1976) Can. J. Physiol. Pharmacol. 54, 27–34) it was shown that the chicken (Gallus domesticus) does not possess a hepatic asialoglycoprotein receptor. In the present study the same conclusion is drawn for the duck (Anas platyrhynchos). For this reason these avian species were used to assess those changes in the distribution and catabolism of human asialotransferrin which take place in the absence of the asialoglycoprotein receptor of the liver.Data obtained from both birds indicate that desialylation does not significantly affect the capillary transfer rate and the extravascular pool size of transferrin but it does shorten the biological life time of the protein. The increases in fractional catabolic rate resulting from desialylation averaged at 18.2% in six chickens and 19.8% in five ducks, these values being close to those reported earlier for bovine, canine, porcine, rabbit and rhesus asialotransferrins in a mammalian system, namely the rabbit.It is concluded that the selective removal of sialic acid residues makes transferrin recognizable as being biologically different from the native protein. As the result of this recognition, asialotransferrin is cleared from the circulation at rates which are slightly but significantly higher than those for the unmodified protein.
Relative importance of alternative pathways of purine nucleotide biosynthesis in Ehrlich ascites tumor cells in vivo
Authors: Smith Camilla M. , Henderson J. Frank
Published: December 2009

Several alternative pathways of purine nucleotide synthesis coexist in cells and the relative importance of each pathway for maintaining purine nucleotide concentrations in cells has been studied. Specific inhibitors were used to block these synthetic routes in Ehrlich ascites tumor cells in vivo and the effect of inhibiting each pathway was evaluated by measuring intracellular purine nucleotide concentrations by high-speed liquid chromatography. The results of this study indicate that adenosine triphosphate and guanosine triphosphate concentrations of Ehrlich ascites tumor cells are maintained primarily by purine biosynthesis de novo although other pathways do make significant contributions.
The subcellular distribution and properties of Crithidia sp. hydrolases with particular reference to pyrophosphate and orthophosphate monoester phosphohydrolases
Authors: McLaughlin J. , Injeyan H. S. , Meerovitch E.
Published: December 2009

A cell fractionation scheme was developed for studying the distribution of certain hydrolases, especially phosphohydrolases, in a Crithidia sp. (Trypanosomatidae). Whilst between 26–56% of the total cellular hydrolase activities were soluble (probably of flagellar pocket origin), a certain percentage, 5–40%, was sedimentable. A particulate fraction obtained after isopycnic density gradient centrifugation (ρ = 1.187–1.241), designated fraction FA/FB, was enriched in various acid hydrolases (relative specific activities 1.33–6.24) and displayed latent phosphohydrolase activities. The density gradient distributions of these hydrolytic enzymes were compared with reference to one another and malate dehydrogenase (mitochondrial marker). From the results obtained it appears that the sedimentable acid hydrolases of Crithidia are associated with a heterogeneous population of subcellular particles. Cytochemical observations on the FA/FB fraction supported this finding and revealed the association of acid phosphatase reaction product with subcellular elements resembling multivesicular bodies.A detailed study of the hydrolytic activity toward both ortho- and pyrophosphate substrates by the soluble, as compared to the FA/FB fractions, revealed the existence of distinct phosphohydrolase activities. It is proposed that these differences in properties are due to the existence of phosphohydrolase isoenzymes and that they in turn relate to a differentiation in the cellular digestive functions of Crithidia.
Acid proteases from species of Mucor. IV. Hydrogen–tritium exchange of Mucor miehei protease
Authors: McBride-Warren P. A. , Rickert W. S.
Published: December 2009

The kinetics of hydrogen–tritium exchange were studied in the range pH 3–5 for both the fully and partially tritiated protein. Exchange constants for an intermediate class and slow class of hydrogens were determined and found to give a parabolic curve characteristic of acid and base catalysis about the observed pHmin of 4.03. The anomalous rate retardation on the acid portion of the curve was attributed to electrostatic interactions which could be evaluated quantitatively from the titration data.Partial tritiation and pH cross-over experiments indicated that the rank order was pH-independent thus eliminating the possibility of a major conformational change. Consequently, the data are most likely explicable in terms of restricted solvent accessibility.
Modification of the regulatory properties of pyruvate kinase of Neurospora by growth at elevated temperatures
Authors: Kapoor M. , O'Brien M. , Braun A.
Published: December 2009

Pyruvate kinase (EC 2.7.1.40) was isolated from Neurospora crassa mycelium grown at 28 °C (PK-28) and at 42 °C (PK-42). The regulatory properties, particularly the response towards the allosteric effector fructose 1,6-diphosphate (FDP), was different in the two enzymes. PK-28 showed an activation by FDP but PK-42, under comparable conditions, appeared to be activated by low concentrations of FDP and inhibited by higher ones. For PK-28, complex formation with FDP results in a lowering of the isoelectric point from 6.40 to 5.50, representing the pI of the unliganded enzyme and that of the complex, respectively. In contrast to this, PK-42 exhibits a weak binding to FDP as suggested by a lack of decrease in the isoelectric point on treatment with comparable concentrations of FDP. Studies with quenching of aromatic residue fluorescence of PK-28 and PK-42, following binding of FDP, indicate that although this ligand binds to both types of enzymes the affinity for the two is vastly different. Dissociation constants of 9.3 μM and 0.1 mM were calculated for the binding of FDP to PK-28 and PK-42, respectively. It is concluded that growth at elevated temperatures induced a conformational change in the pyruvate kinase leading to partial desensitization of the allosteric site. The nature of the factor(s) responsible for this change is not understood at present.
Intracellular distribution of α-fetoprotein and albumin messenger RNAs in developing mouse liver
Authors: Iio Toshihiro , Tamaoki Taiki
Published: December 2009

Intracellular distribution of active mRNAs for α-fetoprotein (αFP) and albumin in fetal and adult mouse liver was studied. Livers were fractionated into nucleus and cytoplasm. The latter was further fractionated by sucrose density-gradient centrifugation into four subfractions, the top fraction containing soluble components, the 1.0 M sucrose layer containing primarily 80S ribosomes, the 1.5 M sucrose layer containing light polysomes and the pellets containing heavy polysomes. RNA was extracted from each fraction and its ability to direct the synthesis of αFP and albumin was determined in a mouse sarcoma 180 cell-free system.Distribution of αFP and albumin mRNAs in fetal mouse liver was similar; 2% in the nucleus, 98% in the cytoplasm, of which more than 90% was found in the polysome fractions. The results suggest that αFP and albumin mRNAs, once formed, are quickly and efficiently utilized for protein synthesis.The major proportion of albumin mRNA in adult mouse liver was also found to be associated with polysomes. However, the amount of translatable αFP mRNA was low in all subcellular fractions examined, suggesting that transcription or processing of αFP mRNA is defective in adult mouse liver.
Modified 5′-nucleotides resistant to 5′-nucleotidase: isolation of 3-(3-amino-3-carboxypropyl)uridine 5′-phosphate and N2,N2-dimethylguanosine 5′-phosphate from snake venom hydrolysates of transfer RNA
Authors: Gray M. W.
Published: December 2009

A procedure for the quantitative measurement of the O2′-methylnucleoside constituents of RNA has recently been developed in this laboratory (Gray, M. W. Can. J. Biochem. 53,735–746 (1975)). This assay method is based on the resistance of O2′-methylnucleoside 5′-phosphates (pNm) (generated by phosphodiesterase hydrolysis of RNA) to subsequent dephosphorylation by venom 5′-nucleotidase (EC 3.1.3.5). In the present investigation, two base-modified 5′-nucleotides, each displaying an unusual resistance to 5′-nucleotidase, have been identified. These compounds have been characterized by a variety of techniques as N2,N2-dimethylguanosine 5′-phosphate [Formula: see text] and 3-(3-amino-3-carboxypropyl)uridine 5′-phosphate (p4abu3U). Because of their resistance to 5′-nucleotidase, [Formula: see text] and p4abu3U are isolated along with the pNm in the mononucleotide fraction of venom hydrolysates of transfer RNA.Under hydrolysis conditions, the stability of p4abu3U is comparable to that of a pNm, allowing quantitative assay of the nucleotide. The proportion (mean ± SD) of p4abu3U in venom hydrolysates of wheat embryo and Escherichia coli tRNA has been determined to be 0.35 ± 0.03 (n = 5) and 0.14 ± 0.02 (n = 4) mol%, respectively. The absence of p4abu3U in venom hydrolysates of yeast tRNA implies the absence of the corresponding nucleoside in yeast tRNA, in agreement with existing data. The variable recovery of [Formula: see text] from venom hydrolysates of wheat embryo and yeast tRNA indicates that under hydrolysis conditions, this base-modified nucleotide is only partially resistant to 5′-nucleotidase. The complete absence of[Formula: see text] in venom hydrolysates of E. coli tRNA is consistent with the known absence of N2,N2-dimethylguanosine in this RNA. These observations demonstrate that resistance to 5′-nucleotidase is a necessary but not sufficient criterion for concluding that a 5′-nucleotide is O2′-methylated.When applied to wheat embryo ribosomal RNA, the analytical methods described in this report failed to reveal any compound having the distinctive charge properties of p4abu3U. It therefore appears that 1-methyl-3-(3-amino-3-carboxypropyl)pseudouridine, recently characterized as a constituent of the 18 S rRNA of Chinese hamster cells (Saponara, A. G. &Enger, M. D. Biochim. Biophys. Acta 349,61–77 (1974)), may not be present in wheat embryo ribosomal RNA.
Kinetic effect of some aliphatic amines on yeast alcohol dehydrogenase
Authors: Dove M. J. , Tsai C. S.
Published: December 2009

Initial rate studies of ethanol oxidation catalyzed by yeast alcohol dehydrogenase (EC 1.1.1.1) were carried out in the presence of varying concentrations of aliphatic amines over the pH range from 8.0 to 10.5. Aliphatic amines either activate or inhibit the enzyme depending on whether the pH is greater or less than 9.5 suggesting that the protonated amines activate and the nonprotonated amines inhibit the enzyme. Aliphatic amines activate yeast alcohol dehydrogenase by decreasing Kb while they inhibit the enzyme by increasing both Ka and Kia. When both protonated and nonprotonated amines are present in solution, either overall activation or inhibition will be observed depending on the relative concentration of the two amine species.
Purification and properties of a carboxylesterase from the liver of tiger shark (Galeocerdo cuvier)
Authors: Scott Keith , Hamilton Susan E. , Zerner Burt
Published: December 2009

A procedure is described for the purification of a carboxylesterase from shark liver, using a chloroform-acetone powder prepared from the liver as the starting material. The yield of purified enzyme is ~50 mg from 530 g of chloroform–acetone powder. The preparation is electrophoretically homogeneous. Active-site titrations with paraoxon gave an equivalent weight of ~83 000. The molecular weight, found from sedimentation equilibrium experiments, is ~80 000. There is no evidence of any association or dissociation of this species. The enzyme shows a marked preference for aryl esters over alkyl esters, in contrast to other carboxylesterases so far studied. The amino acid composition of the purified enzyme is reported.
Identification of liver plasma membrane glycoproteins which bind to 125I-Labelled concanavalin A following electrophoresis in sodium dodecyl sulfate
Authors: Gurd James W. , Evans W. Howard
Published: December 2009

Following electrophoresis of ovalbumin in sodium dodecyl sulfate (SDS) this glycoprotein bound 125I-labelled concanavalin A (Con A). The reaction was specific and proportional to the amount of glycoprotein present on the gel. This technique was used to study the Con-A-binding glycoproteins of liver cell surfaces. Mouse liver plasma membranes were purified and subfractionated to yield two fractions corresponding to the bile canalicular surface and the surface between adjacent hepatocytes (Evans, W. H. (1970) Biochem. J. 116, 833–842). Both fractions bound 125I-labelled Con A, the former binding two to three times more lectin than the latter. Following SDS gel electrophoresis individual membrane glycoproteins reacted with 125I-labelled Con A. Both membrane subfractions yielded qualitatively similar Con A binding profiles, seven binding proteins being present in each. The results are consistent with a generally uniform distribution of glycoproteins over the hepatocyte surface. The reaction of lectins with glycoproteins following SDS gel electrophoresis should find general application in the study of membrane composition.
Subunit studies of coupling factor 1 of bean chloroplasts
Authors: Silvanovich M. P. , Hill R. D.
Published: December 2009

A bean chloroplast coupling factor (CF1) with latent Ca2+-dependent ATPase activity was studied. Immunodiffusion of bean (Phaseolus vulgaris) chloroplast and etioplast coupling factors and spinach coupling factor against antiserum to spinach coupling factor showed partial identity of the bean coupling factor with that of spinach. An immunoelectrophoretic comparison, under dissociating conditions, of bean leaf extracts and spinach extracts containing CF1 subunits (as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis) gave identical results for both extracts. At least six distinct polypeptide species were found. The major species had molecular weights of 42 000, 59 000 and 63 000 daltons. Amino acid analysis of electrophoretically purified bean CF1 gave results similar to those published for spinach CF1.
The synthesis and some pharmacological properties of [2-L-DOPA]-oxytocin
Authors: Ferrier B. M. , Branda L. A.
Published: December 2009

The first reported synthetic analogue of a naturally occurring peptide with a residue of L-3,4-dihydroxyphenylalanine (L-DOPA) was prepared by coupling N-carbobenzoxy-S-benzylcysteinyl-L-DOPA azide with isoleucylglutaminylasparaginyl-S-benzylcysteinylprolylleu-cylglycinamide. The protecting groups were removed from the resultant nonapeptide derivative by sodium in liquid ammonia and the peptide analogue was formed by short term oxidation of the dithiol-containing compound. It was isolated by sequential partition chromatography and exclusion chromatography on Sephadex G-25. It was unstable at neutral or alkaline pH. [2-L-DOPA]-oxytocin was found to possess a minimum milk-ejection-like activity of 54 ± 9 U/mg and uterotonic activity of 26 ± 4 U/mg. These potencies are approximately 12% and 5% of the corresponding potencies of oxytocin.
Comparative study of the lipid composition of rabbit and lobster sarcoplasmic reticulum
Authors: Madeira Vitor M. C. , Antunes-Madeira M. C.
Published: December 2009

Sarcoplasmic reticulum (SR) membranes isolated from rabbit and lobster muscles have similar phospholipid classes, but they differ in plasmalogen content. The plasmalogenic species are mostly distributed among phosphatidylethanolamines (PE's) and make up about 62% of the total in rabbit SR and about 46% in lobster membranes. Lobster SR phospholipids contain large amounts of polyunsaturated fatty acids which are present in low amounts in rabbit membranes. The total unsaturated fatty acids of phosphatidylcholines (PC's) represent about 53% and 73% of the total fatty chains for rabbit and lobster SR, respectively. The values found for PE's were about 56% and 64%., respectively. Furthermore, lobster membranes contain significant amounts of PC and PE molecular species with unsaturated fatty acids in positions 1 and 2, whereas rabbit SR contain low amounts.
Sulfhydryl analogues of adenosine diphosphate: chemical synthesis and activity as platelet-aggregating agents
Authors: Stone J. V. , Singh Raj K. , Horák H. , Barton P. G.
Published: December 2009

2-Thioadenosine 5′-diphosphate (2-SH ADP), 2,2′-dithiobisadenosine 5′-diphosphate (2,2′-(S-ADP)2), 8-thioadenosine 5′diphosphate (8-SH ADP), and 6-mercaptopurine riboside 5′-disphosphate (6-MPRDP) were synthesized as potential affinity labels for ADP receptors on the blood-platelet membrane. The mean relative activities of these compounds in aggregating human platelets suspended in homologous plasma were 155% (2,2′-(S-ADP)2), 74% (2-SH ADP), 0.65% (8-SH ADP), and 0.08% (6-MPRDP). The mean relative activities against washed platelets were 249% (2,2′-(S-ADP)2) and 115% (2-SH ADP), whereas no aggregation occurred with 8-SH ADP or 6-MPRDP. The last two compounds were found to be weak inhibitors of ADP-induced aggregation. Therefore, thio-substitution at position 2 followed by oxidation to a disulfide appears to be the most promising approach to further studies of affinity labelling of membrane ADP-receptors.
Pyruvate dehydrogenase activity in liver and brown fat of the developing rat
Authors: Bailey Kathryn , Hahn Peter , Palaty Vladimir
Published: December 2009

The total activity of pyruvate dehydrogenase (EC 1.2.4.1) and the fraction of the enzyme in the active form were assayed in brown fat and liver throughout the development of the rat.In brown adipose tissue, the total activity increased until the late suckling period. After weaning, a decrease was noted. The fraction of the enzyme in the active form did not increase until after 10 days of age, reached its highest level in the late suckling period and remained at this level after weaning.Pyruvate dehydrogenase in liver decreased in both total activity and percentage activity in the early neonatal period. Both parameters increased after this period, reaching their highest levels in the late suckling period.In both fetal liver and fetal brown fat, the total activity of pyruvate dehydrogenase was increased by in vitro incubation with insulin.
Properties of the citrate transporter in rat heart: implications for regulation of glycolysis by cytosolic citrate
Authors: Cheema-Dhadli Surinder , Robinson Brian H. , Halperin Mitchell L.
Published: December 2009

The efflux of [14C]citrate from rat heart mitochondria was significantly greater with L-malate as the extramitochondrial substrate as compared with [12C]citrate, isocitrate or phosphoenolpyruvate. The concentration of L-malate required for half-maximal rate of efflux of citrate was 0.45 mM and the maximum velocity was 0.36 nmol min−1 mg−1 mitochondrial protein at 23 °C. This citrate transporter was inhibited by 1,2,3-benzenetricarboxylate and palmitoyl-CoA but not to the same extent as these compounds inhibit the tricarboxylate carrier in rat liver mitochondria. The apparent inability of these mitochondria to transport citrate in the inward direction necessitates the presence of a cytosolic citrate removal pathway. We propose that the enzymes of this pathway in rat heart could be ATP citrate (pro-3S)-lyase (EC 4.1.3.a) and carnitine acetyltransferase (EC 2.3.1.7), both of which we demonstrate to have adequate activity in both the fed and fasted state.An hypothesis has been put forward to account for the inhibition of rat heart phosphofructokinase by citrate in the fasted state incorporating these properties of the citrate transporter and ATP citrate (pro-3S)-lyase.
The absence of cell-specific histone in erythroid cells from rabbit marrow
Authors: Adams G. H. M. , Neelin J. M.
Published: December 2009

The histone complements of erythroid cells from anemic rabbit bone marrow and cell fractions enriched in orthochromatic erythroblasts were examined using a variety of techniques. None of these methods revealed the presence of a histone comparable to H5, the erythrocyte-specific histone of birds and fish. Purified histones H1, H2A, H2B, H3 and H4 from rabbit marrow nuclei showed no unusual amino acid compositions.
Inhibition by saccharin of glucose-6-phosphatase: effects of alloxan in vivo and deoxycholate in vitro
Authors: Lygre David G.
Published: December 2009

Inhibition by saccharin of rat liver glucose-6-phosphatase (EC 3.1.3.9) generally decreased as the pH increased in the range pH 4–8. This pattern was exhibited by homogenates from control and alloxan-treated animals assayed each in the absence and presence of 0.2% (w/v) deoxycholate. Saccharin inhibited in competitive fashion with respect to glucose-6-phosphate (glucose-6-P). There was a small increase in Km (glucose-6-P) but not Ki (saccharin) values in alloxan-treated rats when assays were conducted in the absence of deoxycholate. In the presence of this detergent there was no significant difference in these kinetic parameters between the alloxan-treated and control groups. Deoxycholate decreased Km (glucose-6-P) and increased Ki (saccharin) values. Calculations using these kinetic parameters indicate that, under usual hepatic glucose-6-P concentrations and relatively high levels of saccharin in liver, the inhibition by saccharin of glucose-6-phosphatase is unlikely to be of major significance in vivo.
The binding of phytohemagglutinin M to rat spleen lymphocytes. Quantitative studies
Authors: Dupuis G.
Published: December 2009

Phytohemagglutinin M (PHAM) has been purified from the commercial mixture of proteins produced by Phaseolus vulgaris, using a Sepharose–thyroglobulin column. The protein gave one band on gel electrophoresis and two bands on SDS–gel electrophoresis (mol. wt. 33 700 and 32 100, respectively). Molecular weight determination by ultracentrifugation gave a value of 61 200 ± 700. The protein had a minimum sugar content of 16%. Binding studies of PHAM to purified rat spleen lymphocytes have been performed at 0, 25, and 37 °C. It was shown that the cells bound about the same amount of lectin at 0 and 37 °C, but less protein was bound at 25 °C. The binding phenomenon showed saturability at all temperatures. Data were analyzed by Scatchard plots and two kinds of binding sites were found. High-affinity sites and low-affinity sites have been characterized in terms of association constants and (apparent) number. It was also shown that cells treated with trypsin or sodium azide bound less lectin. Bound concanavalin A did not appear to affect the amount of bound PHAM, but its influence was reflected in the value of the association constant for the binding of PHAM. Unlabelled PHAM was shown to displace radioactive PHAM from the cells, but could not remove bound concanavalin A. The significance of these results is discussed in terms of the fluid plasma membrane model and cellular metabolism.
Differential effects of pyridoxal 5′-phosphate on lysine residues in rabbit and sturgeon muscle aldolases
Authors: Marie Alain L.
Published: December 2009

Pyridoxal 5′-phosphate (PLP) in aqueous solutions can form a Schiff base complex with 14 and 16 lysine residues of rabbit and sturgeon muscle aldolases (EC 4.1.2.13), respectively. Although the mechanism of their interaction with PLP should be the same, these residues can be differentiated into three families on the basis of their inhibition constant Ki and rate constant k. The lysine residues of one of these families do not react with PLP in the presence of the substrates. Therefore, they are assumed to be part of the active center.In the sturgeon muscle aldolase, 3.7 substrate protected lysine residues are present. Rabbit aldolase, although tetrameric, contains only 2.8 substrate protected lysine residues. This suggests that one active center of this enzyme may be 'buried'.Structural studies showed the following sequence around the substrate protected lysine residues, in the rabbit aldolase: Gly-(Gly2, Val3)-Pyridoxyl Lys-Ile-Asp-Lys.
Sensitivity of glucose-6-phosphate dehydrogenase activity to saturated and unsaturated fatty acids
Authors: Vanni P. , Vincieri F. , Vincenzini M. T.
Published: December 2009

The effect of a number of saturated and unsaturated fatty acids on purified glucose-6-phosphate dehydrogenase (G6PDH) (EC 1.1.1.49) enzyme of yeast was studied. Saturated and unsaturated fatty acids were found to be strong inhibitors of G6PDH activity, the former being noncompetitive inhibitors and the latter being competitive inhibitors.
The selective extraction of histones from rye chromatin
Authors: LaRue Hélène , Pallotta Dominick
Published: December 2009

The selective extraction of histones from rye chromatin was studied using three different methods. Extractions with NaCl–phosphate buffers atpH 5.5 gave results similar to those already obtained with other types of chromatin. Histone H1 was selectively extracted with 0.6 M NaCl –0.001 M PO4, while the selectivity of dissociation of the other fractions was reduced at higher NaCl concentrations. The use of phosphate–urea buffers at pH 5.5 also revealed that the histones were dissociated at the same concentrations as were calf thymus histones. Histone H1 was extracted with 0.5 M PO4 – 1 M urea; H1, H2A, and H2B were extracted with 0.8 M PO4 – 2 M urea; and all histones were removed with 0.8 M PO4 –5.3 M urea. It was, however, observed that the dissociated rye histones H2A and H2B were unstable in these buffers. This instability was maximum in the presence of 3 M urea, where both histones were absent from the extracted proteins and the residual nucleoproteins. Finally, a solution of 30% ethanol −0.35 M NaCl – 6 M urea produced a rye nucleoprotein fraction containing only histone H1.
The amino acid sequence of wheat β-purothionin
Authors: Mak A. S. , Jones B. L.
Published: December 2009

The complete amino acid sequence of β-purothionin, a low molecular weight, very basic, protein isolated from wheat endosperm material, has been determined. β-purothionin is toxic to some bacteria, to yeasts, and to animals when injected. The protein contains 45 amino acid residues and has a molecular weight of 4913. The 8 cysteine and 10 basic residues are distributed throughout the molecule. The primary structure of the protein shows considerable homology to those of the viscotoxins, which are toxic, small, basic proteins found in the leaves and stems of European mistletoe (Viscum album L.).
Chloroplastic proteins of wheat and rye grown at warm and cold-hardening temperatures
Authors: Huner Norman P. A. , Macdowall Fergus D. H.
Published: December 2009

Soluble proteins and membrane polypeptides were separated from chloroplasts isolated intact from a cultivar each of spring wheat, winter wheat, and more freeze-resistant rye, and changes in them associated with cold hardening were detected by means of polyacrylamide gel electrophoresis. No drastic changes in chloroplast membrane polypeptides occurred during growth at low temperatures in the three cultivars. However, subtle changes were evident in the soluble chloroplast protein fraction. In this fraction at least one varietal difference was discernable, yet all cultivars produced a new protein band of lowest mobility during growth at low temperatures. After the preparations were fractionated by Sephadex G-50 all unhardened plant material displayed two peaks in the region of the fraction I protein band, whereas all cold-hardened material displayed one peak. A different band of soluble protein was present only after cold hardening in Kharkov wheat and Puma rye, and was not present in extracts from the cold-grown spring wheat.
Amino acid sequence of penicillopepsin. I. Isolation and characterization of the chymotryptic peptides
Authors: Kurosky Alexander , Hofmann Theo
Published: December 2009

The amino acid sequences of 48 peptides obtained from a chymotryptic digest of the mould acid protease, penicillopepsin (EC 3.4.23.7), have been determined. These peptides established the sequences of 26 unique fragments of up to 28 residues in length. The 28-residue fragment was identified as the N-terminal region. The C-terminal region is represented by a 13-residue fragment. The amino acids contained in these fragments account for some 85% of the residues of the enzyme.
Amino acid sequence of penicillopepsin. III. Isolation and characterization of amino terminal, tryptic, and tryptophanyl peptides
Authors: Harris C. Ian , Rao Leticia , Shutsa Paul , Kurosky Alexander , Hofmann Theo
Published: December 2009

The amino acid sequences of peptides isolated from a tryptic digest of penicillopepsin (EC 3.4.23.7), a subtilisin (EC 3.4.21.14) digest of maleylated penicillopepsin, and a chymotryptic digest of penicillopepsin modified with dinitrophenylsulfenyl (DNPS) chloride have been determined. The first two digests identified four of the five lysyl residues of the enzyme as well as the N-terminal peptide. The third digest provided overlaps at three of the tryptophanyl residues. The DNPS-tryptophan peptides were isolated on an affinity column prepared by coupling dinitrophenyl antibody raised in sheep to cyanogen bromide-activated Sepharose.
Four- and five-step kinetic models of lactate dehydrogenase
Authors: Borgmann Uwe , Laidler Keith J. , Moon Thomas W.
Published: December 2009

A five-step model for the reaction catalyzed by beef heart lactate dehydrogenase (EC 1.1.1.27) reconciles differences observed in the four-step model if pre-steady-state data in the forward direction are compared with similar data in the reverse direction. The relationship between the four- and five-step models indicates what problems can develop when an incomplete model is proposed. Nevertheless, there are advantages to using the less complicated four-step model when comparing the molecular kinetics of enzymes catalyzing the same reaction but obtained from different sources.
Purification of an exo-1,3-β-glucanase from Candida utilis
Authors: Villa T. G. , Notario V. , Benítez T. , Villanueva J. R.
Published: December 2009

An exo-1,3-β-glucanase (EC 3.2.1.—) has been purified from the culture fluid of the yeast Candida utilis, and its biochemical properties have been studied. The amino acid analysis revealed a high content of acidic amino acids. The purified enzyme had 20% carbohydrate and a net negative charge showing higher affinity for laminarin than for p-nitrophenyl-β-D-glucopyranoside and yeast cell-wall 1,3-β-glucans. In addition, the enzyme hydrolyzed the substrates starting from the nonreducing ends, releasing glucose as the exclusive hydrolysis product. The enzyme activity was strongly inhibited by lactones and also by some heavy-metal ions.
Synthesis of guanosine 5′-triphosphate,3′ -diphosphate in a spoT strain of Escherichia coli
Authors: Chaloner-Larsson Gillian , Yamazaki Hiroshi
Published: December 2009

A spoT stringent strain of Escherichia coli rapidly accumulates guanosine 5′-triphosphate,3′-diphosphate (pppGpp) immediately after the onset of isoleucine starvation. Subsequently, its level rapidly falls, as guanosine 5′-diphosphate,3′-diphosphate (ppGpp) continues to rise to the maximum value, which is abnormally high compared with that in the spoT+ strain. The ppGpp level in the spoT strain never reaches a steady state as it does in the spoT+ strain. Immediately after starvation, pppGpp and ppGpp are labeled with [3H]guanosine at a similar differential rate in both the spoT and spoT+ strains, suggesting that the two strains synthesize these nucleotides by the same pathway. However, by 15 min after starvation, the synthesis of these nucleotides is nearly halted in the spoT strain, and is greatly reduced in the spoT+ strain. Since ppGpp is labeled with [3H]guanosine more slowly than pppGpp in the starved spoT+ strain, ppGpp cannot be a precursor of pppGpp. The kinetics of the GTP level during starvation suggests that GTP is a precursor of pppGpp. The observed differences between the spoT and spoT+ strains can be explained by postulating, firstly, that ppGpp negatively controls the conversion of GTP to pppGpp, which is subsequently converted to ppGpp; secondly, that a catabolite of ppGpp negatively controls the conversion of pppGpp to ppGpp; and thirdly, that the spoT mutation primarily reduces the rate of ppGpp catabolism.
Circular dichroism studies of sheep β-lipotropic hormone
Authors: St-Pierre Serge , Gilardeau Claude , Chrétien Michel
Published: December 2009

The far ultraviolet circular dichroism spectra of sheep β-lipotropic hormone (β-LPH) were recorded under different conditions of pH, temperature, salt concentration, and solvent composition. Results confirm the stability of the hormone in strong basic or acidic solutions; moreover, temperatures up to 50 °C do not seem to affect noticeably the conformation of β-LPH. However, increasing the NaCl concentration or addition of dioxane in the solution brings about a conformational transition of the chain, interpreted as an increase in the helical content. The method of Yang (Chen, Y. H., Yang, J. T. &Martinez, H. M. (1972) Biochemistry 11, 4120–4131) was used to compute the proportion of helical, β, and unordered forms of the hormone chain. The proportions are compared with those obtained from Fasman's predictive method (Chou, P. Y. &Fasman, G. D. (1974) Biochemistry 13, 211–221 and Chou, P. Y. &Fasman, G. D. (1974) Biochemistry 13, 222–245) based on the known amino acid sequence of β-LPH.
Further studies on aspartate transcarbamoylase: molecular weight of the c3r6 complex and analysis of succinate inhibition in the native enzyme
Authors: Chan William W.-C.
Published: December 2009

The complex which is formed when excess regulatory subunits (r2) of aspartate transcarbamoylase (EC 2.1.3.2) are added to a dilute solution of the catalytic subunit (c3) has been studied by gel-filtration on Sephadex G-200. The elution volume indicates a Stokes' radius of between 5.42 and 5.92 nm, depending on the method of calculation. Using the sedimentation coefficient of 7.7 S previously determined, the molecular weight is estimated to be close to 200 000, in support of the c3r6 structure proposed earlier for the complex. The calculated frictional coefficient indicates abnormal hydrodynamic properties which are probably due to unusual structure characteristics.The pattern of succinate inhibition of native aspartate transcarbamoylase has also been analyzed. At low concentrations, succinate activates the enzyme, presumably by converting it from the taut state to the relaxed (R) state. Further increase in the succinate concentration leads to competitive inhibition of the R state. Using a novel procedure for analysis of the data, the Michaelis constant for aspartate of the R state has been estimated to be about 7 mM. This value is close to the Km of c3r6 for aspartate, measured under identical conditions. The result therefore provides further evidence suggesting that the c3r6 complex resembles the R state of the native enzyme.
Photosynthesis, water relations, and growth of two hybrid Populus genotypes during a severe drought
Authors: Dickmann Donald I. , Liu Zhijun , Nguyen Phu V. , Pregitzer Kurt S.
Published: December 2009

During the 1988 growing season in East Lansing, Michigan, United States, only 1.53 cm of rain fell from mid-May to mid-July, causing a severe drought. Then, beginning in mid-July, a period of near-record precipitation commenced; 30.4 cm of rain fell from July 19 to October 4. Growth, photosynthesis, and water relations of hybrid poplar cultivars 'Eugenei' and 'Tristis', which had been established in the spring of 1987 in 114-L plastic pots buried in the ground, were measured on several sunny days during the 1988 growing season. Pots were irrigated at two different rates, and half the pots received supplemental nitrogen fertilizer. On a seasonal basis, photosynthesis and water-use efficiency in both genotypes peaked in early July and declined thereafter. Stomatal conductances were low during the drought but increased substantially when the rains commenced. Whereas nitrogen level had little effect on leaf physiology, the low water treatment produced significant reductions in photosynthesis and conductance. Diurnal measurements were made on June 17 and July 12. On both days photosynthesis and conductances were higher in 'Tristis' than in 'Eugenei', especially for plants in the high water treatments and on July 12, the most extreme period of the drought. Drought produced both stomatal and mesophyll limitations to photosynthesis in both clones, though these responses were more pronounced in 'Eugenei'. This clone also showed very low water-use efficiencies in the low water treatment on July 12. Even though the physiology of 'Eugenei' was more impacted by drought than 'Tristis', it still produced two to three times more biomass over the 2-year period of the study than did 'Tristis'.
The applicability of the pipe model theory for the prediction of foliage biomass in trees from natural, untreated black spruce stands
Authors: Robichaud Edgar , Methven Ian R.
Published: December 2009

Trees were sampled from 26 black spruce (Piceamariana (Mill.) B.S.P.) stands across New Brunswick and within the boreal forest of Quebec to test the validity of the pipe model theory for sampling purposes. Trees were sampled from a wide range of ages, site qualities, densities, and social classes for determination of foliage biomass and sapwood cross-sectional areas at breast height and at the base of the live crown. A strong relationship was found between sapwood cross-sectional area and foliage biomass across the range of conditions. The y-intercepts for these regression equations, based on the untransformed data, were not significantly different from zero (P < 0.05). Partial correlation analysis indicated no significant relationship between the foliage biomass and tree age, site quality, or stand density but confirmed the strong relationship with sapwood cross-sectional area. Suppressed and intermediate social classes followed a similar relationship as dominant trees. Regression equations developed from this study were similar to those determined for spruce species and supported the use of sapwood cross-sectional area as a predictor of foliage biomass for black spruce.
Upgrading germinability and vigour of jack pine, lodgepole pine, and white spruce by the IDS technique
Authors: Downie Bruce , Wang Ben S.P.
Published: December 2009

The IDS (incubation–desiccation–separation) technique, designed to upgrade germinability and vigour of conifer seed lots, was tested on various seed lots of white spruce (Piceaglauca (Moench) Voss), lodgepole pine (Pinuscontorta var. latifolia Engelm.), and jack pine (Pinusbanksiana Lamb.). The effect on germinability of redrying separated seeds to storage moisture content (approx. 5% fresh weight) and of accelerated ageing was also investigated. Separation resulted in significant increases in germinability for four of five lodgepole pine, three of four jack pine, and two of five white spruce seed lots. Redrying usually had no significant effect on germinability of separated seeds, and its effect was not predictable. Accelerated ageing decreased the mean germinability of all seed lots and fractions. Although the mean index of ageing was usually not significantly different between the control and bottom fraction (live seeds) for any species, the surface fraction (dead and dying seeds) usually had a significantly higher index of ageing. The IDS technique is effective for upgrading the germinability of a portion of a seed lot of lodgepole pine and jack pine but must be modified if it is to work well with white spruce.
Factor substitution and economies of scale in the southern Ontario hardwood sawmilling industry
Authors: Puttock G.D. , Prescott D.M.
Published: December 2009

An analysis of pooled data reveals that a nonhomothetic transcendental logarithmic cost function provides an appropriate representation of the hardwood lumber manufacturing industry in southern Ontario. In this study, total cost was specified as a function of mill output; the input prices for wood, labour, and energy; and a measure of mill capacity. All own-price elasticities have the expected negative sign. All input pairs are found to be substitutes, with labour and energy displaying the strongest substitutability relationship. There are economies of scale that have yet to be exploited by sawmills producing less than 16 × 106 board ft (1 board ft = 2.360 dm3) of lumber annually. Scale economies are fully exhausted for mills with annual output greater than this value.
Introduction of black walnut in southern Quebec: evaluation of 21-year-old full-sib families
Authors: Li Peng , Parrot Louis , Bousquet Jean
Published: December 2009

Black walnut (Juglansnigra L.) was introduced in the Québec City area 110 years ago. In the present study, we investigated performance of five full-sib families from controlled crosses among five selected cold-hardy parent trees of the introduced population. The number of seeds set per pollination bag averaged three, and seed germination was high (90%). At one fertile site close to the original plantation, the families showed normal growth, high survival rate, and good adaptability, as indicated by minimal frost damage. The average height was 3.1 m at 11 years, and 8.7 m at 21 years, reaching the height observed in native stands of black walnut. Therefore, the parent trees and their progenies could be used to produce seed for planting on similar sites. The results of this study demonstrated the importance of cold hardiness when introducing species into the northern temperate climatic zone.
Possible Distribution of Potential Inside Corroding Crevices
Authors: Engelhardt George , Macdonald Digby D.
Published: December 2009

In this paper, the case when the potential distribution inside a corrosion cavity obeys Ohm's law is considered. Mathematically, the potential drop in the crevice is described by a Poisson-type equation with a non linear source term. It is shown that, in the general case, this problem has more than one solution, indicating that the potential and current distributions in the crevice depend not only on the metal potential, solution conductivity, and geometry of the crevice, but also on the history of crevice initiation. The absence of a unique solution of the charge transfer equation can explain the fact that both passive and active crevices with approximately equal geometrical parameters are often observed simultaneously on the same metal surface. It is further shown that, in the general case, it is impossible to neglect the potential drop in the external environment when quantitatively describing crevice corrosion.
A Study on the Accuracy of the Tafel Extrapolation Method in HCl
Authors: Poorqasemi Eqbal , Haqdar Fatemeh , Abootalebi Omid
Published: December 2009

Accuracy and validity of the Tafel extrapolation method for determining corrosion rates of carbon steel in 1,2 and 3M HCl solutions open to air is discussed. Corrosion rates obtained from polarization experiments were compared with that of weight loss method. For analysing data obtained from polarization experiments electrochemical impedance spectroscopy (EIS) measurements were performed before polarization experiments. The results showed that formation of a corrosion product film and increasing the polarization resistance (Rp) of this film with time cause the corrosion rates obtained from Tafel extrapolation tend to be higher than corrosion rates obtained from weight loss test.
Biphasic Numerical Simulation of a Rotating Disc Electrochemical Cell
Authors: Real-Ramirez Cesar Augusto , Palomar-Pardavé Manuel , Rodriguez-Torres Israel , Hoyos-Reyes Luis , Gonzalez Jesus
Published: December 2009

On electrochemical studies involving forced convection, the cell with rotating disc is the most widely used. Traditionally, Levich equation is used to interpret the information obtained from physical experiments. However, electrochemical results can be accurately interpreted through this equation only if the velocity field near the electrode active face is in accordance with the ideal behavior described by Cochran. In this work, the Computational Fluid Dynamics (CFD) technique was employed to determine the effect of the distance between the electrode active surface and the cell bottom on the cell inner hydrodynamic behavior. Biphasic 3D numerical simulations were performed using the commercial software Fluent. Numerical results were validated with experimental data. A simple rule for the optimal distance between the electrode active surface and the cell bottom is presented in this work.