bluuebunny/crossref_metadata_2025 huggingface dataset:
Cytokinin Activity of a Group of Ureidopurine Derivatives Related to the tRNA Component, N-(Purin-6-ylcarbamoyl)threonine
Authors: Dyson W. H. , Hall R. H. , Hong C. I. , Dutta S. P. , Chheda G. B.
Published: December 2009

Several ureidopurine derivatives have been tested for cytokinin activity in a soya bean callus assay system. N-(Purin-6-ylcarbamoyl)threonine (Ade-CO-Thr), a naturally occurring component of tRNA, is inactive in the assay. Analogues of Ade-CO-Thr having unmodified hydrocarbon side chains are active; optimal activity is associated with tert-butylureidopurine. In the homologous straight chain series n-butylureidopurine is the most active. Introduction of −COOH and/or −OH groups to analogues with otherwise active alkyl chains negates activity.The phenylureidopurine (PUP) derivative is barely active itself, though ortho-halogenated derivatives (o-chloro-, o-fluoro-PUP) are the most potent ureidopurines known. Biological activity decreases rapidly as the electronegative halide is moved from the ortho to the meta position, and lost entirely in the para position. Replacement of the ortho halide with a non-electronegative group (methyl) greatly reduces activity. Molecular models reveal that Ade-CO-Thr and o-chloro-PUP have nearly identical side-chain bulk. The carboxyl groups of Ade-CO-Thr and the chlorine atom of o-chloro-PUP occupy the same position relative to the electronegative carboxyl oxygen of the urea bridge. It is proposed that Ade-CO-Thr has a growth regulatory role in the intact organism, but that exogenous Ade-CO-Thr may be unable to reach the active site.
The Effect of Single and Repeated Injections of Adrenocorticotropin on Lipids in Rat Adrenals
Authors: Palkovič M. , Macho L.
Published: December 2009

A study of the influence of adrenocorticotropin (ACTH) on various adrenal lipid fractions of intact rats indicated that single and repeated doses (3 or 10 days administration) of ACTH had a lipolytic effect on adrenal fat. A decrease of cholesterol and triglyceride content of the adrenal gland after a single dose of ACTH was observed. However, after 3 days injection of ACTH, only the cholesterol concentration diminished. The triglyceride content was the same as that in saline-injected control animals. On the other hand, a significant increase in triglycerides was noted in adrenal gland after 10 days of ACTH injections. No substantial changes in unesterified fatty acids and phospholipids were noted in response to a single dose, or to repeated doses of ACTH.
The Assay of Cholesterol Sulfate in Biological Material by Enzymatic Radioisotopic Displacement
Authors: Bleau G. , Chapdelaine A. , Roberts K. D.
Published: December 2009

A technique is described for the measurement of cholesterol sulfate (CS) which is based upon the displacement of labelled CS from a placental sulfatase enzyme system by the addition of unlabelled CS isolated from various biological sources.From the extent of this displacement by unknown samples of CS and by reference to standard curves, the concentration of CS in the biological samples can be calculated. This assay method is relatively simple, rapid, and sensitive (nanogram level) and provides values which are in good agreement with those obtained by a double isotope derivative assay. Levels of CS in human plasma, erythrocytes, semen, and saliva have been determined. This sterol sulfate appears to be a ubiquitous entity although its biological function remains to be determined. Certain aspects of its possible physiological role in the organism are discussed.
The Specific Chemical Cleavage of Pyrophosphate Diesters
Authors: Rutherford G. , Morgan A. R.
Published: December 2009

A recent model for DNA replication postulates a pyrophosphate diester at the growing point linking the two daughter strands. This stimulated the development of methods for specifically cleaving pyrophosphate diesters leaving phosphodiester groups intact. Three methods have been found for cleaving pyrophosphate diesters. These methods should have applications in polynucleotide synthesis and in the characterization of any phosphate-containing compounds.
Studies on Isolated Brain Nuclear DNA-Dependent RNA Polymerase
Authors: Singh Vijendra K. , Sung S. C.
Published: December 2009

DNA-dependent RNA polymerase, which was isolated from beef brain nuclei, was stimulated by Mn2+ and Mg2+. The polymerase was about four times as active with Mn2+ as with Mg2+ but both of these divalent cations were required for maximum activity. KCl stimulated the enzyme activity with an optimum concentration around 0.2 M. The stimulation by KCl was much more pronounced in the presence of Mn2+ or Mn2+ plus Mg24 than in the presence of Mg2+ alone. Spermidine and spermine also stimulated the RNA polymerase activity and this stimulation was much greater in the presence of Mn2+ than in the presence of Mg2+ or both together. With Mn2+ plus Mg2+, spermidine had little or no stimulatory effect when heat-denatured DNA served as template, whereas with Mn2+ alone, spermidine markedly stimulated the enzyme in the presence of either native or heat-denatured DNA. The effect of spermidine was different with Mg2+ alone. The enzyme was inhibited as much as 75% by actinomycin D and almost completely by α-amanitin but not by rifampicin. Yeast RNA inhibited the enzyme activity considerably while spermidine appeared to overcome and prevent this inhibition of RNA polymerase.
The Precipitation of Polymerized Silicic Acid by Urine Protein: A Possible Mechanism in the Etiology of Silica Urolithiasis
Authors: Bailey C. B.
Published: December 2009

The precipitability of polymerized silicic acid by gelatin and urine protein was tested with solutions containing various combinations of silicic acid, protein, and salt. The ranges of pH and of the concentrations of the constituents in the mixtures were like those normally encountered in the urine of cattle on a calculogenic diet.Silicic acid precipitated in the absence of protein only at the highest concentrations of silicic acid and salt and at the highest pH. Although gelatin precipitated aged silicic acid in the absence of salt, precipitation of freshly prepared silicic acid by either urine protein or gelatin required the presence of salt. The amount of silicic acid precipitated by urine protein increased as the concentrations of the silicic acid, protein, and salt increased. There was an interaction between the effects of pH and salt, the greatest amount of precipitate tending to form at higher pH as salt concentration increased.These results suggest that urine protein, by affecting the solubility of polymerized silicic acid, contributes to the formation of siliceous urinary calculi.
Model Lipid Membrane Permeability to ATP
Authors: Petkau A. , Chelack W. S.
Published: December 2009

A model phospholipid membrane separating two aqueous compartments was measured for permeability to 3H-ATP by diffusion. No diffusion lag time was demonstrated but the permeability coefficient was dependent on the ionic composition of the aqueous medium. In 0.1 M NaCl and distilled water the permeability coefficient was 6.78 × 10−7 cm/s and 1.41 × 10−7 cm/s, respectively, while in 0.5 mM MgCl2 it varied from a minimum of 0.25 × 10−7 cm/s to a maximum of 6.87 × 10−7 cm/s, depending on the concentration difference of 3H-ATP across the membrane.In 0.1 M NaCl the diffusion process had an activation energy of 1 kcal/mol while in 0.5 mM MgCl2 it exhibited a saturation characteristic which was attributed to space charge effects within the membrane. In 0.5 mM 2,4-dinitrophenol the permeability of the membrane to 3H-ATP was inhibited.
Malate Dehydrogenase in Maize Endosperm: The Intracellular Location and Characterization of the Two Major Particulate Isozymes
Authors: Hayden D. B. , Cook F. S.
Published: December 2009

Multiple molecular forms of malate dehydrogenase (MDH) were detected in several tissues of maize using polyacrylamide gel electrophoresis. An investigation of MDH in 14-day-old endosperm tissue revealed that the two major isozymes were associated with particulate cell fractions, the mitochondria and glyoxysomes. Preparations of these two particulate isozymes, designated m-MDH and g-MDH, were obtained by anion-exchange chromatography and several physical and kinetic parameters were measured. Both isozymes had approximately the same Stokes radius (34 Å) but were catalytically distinct. Differences were found in their relative rates of reaction with NAD and two of its analogues (thionicotinamide-NAD and acetylpyridine-NAD) as well as in changes of Km (oxalacetate) with pH. The possible physiological roles of these two isozymes are discussed.
Effects of Cerebral Stimuli on Adenine Incorporation into Nucleotides and RNA in Brain Slices from the Rat
Authors: Glick N. B. , Quastel J. H.
Published: December 2009

Comparisons have been made of the rates of incorporation of [8-14C]adenine into RNA and of the specific activities of labelled ATP, in rat brain cortex slices incubated under conditions affecting nucleotide and RNA synthesis.The presence of 50 mM KCl in the incubation medium causes a considerable reduction of the rate of [8-14C]-adenine incorporation into RNA, with no diminution of the specific activity of the cerebral ATP or of the rate of nucleotide formation from adenine. It is inferred that cerebral RNA synthesis is suppressed by 50 mM KCl in the incubation medium.When K+ is omitted from the incubation medium or in the presence of 198 mM NaCl or 5 mM sodium L-glutamate, both the rate of [8-14C]adenine incorporation into RNA and the specific activity of cerebral ATP are diminished to approximately the same extent. This suggests that the process of RNA synthesis in the brain tissue is but little affected either by the increased ceil concentration of Na+ or by the diminished ATP concentration that obtain under these incubation conditions. The process, however, of [8-14C]adenine incorporation into cell nucleotides is markedly suppressed.The presence of protoveratrine (10 μM) causes at least 40% reduction in the rates of [8-14C]adenine incorporation into both RNA and nucleotides with little reduction in the specific activity of the cerebral ATP. The effects of protoveratrine are abolished by tetrodotoxin, indicating that the effects of protoveratrine are confined to the neurons.It is concluded that reductions of the specific activity of cerebral ATP derived from labelled adenine are due to the diminished rates of nucleotide formation from adenine that occur under specific incubation conditions. Such reductions may give rise to the observed diminutions in the rates of incorporation of labelled adenine into RNA. The relatively small fail in the specific activity of isolated ATP after incubation of brain tissue in the presence of protoveratrine is attributed to the localization of the effects of this drug to the neurons, in which the content and specific activity of ATP are suppressed, while those in the glia are undiminished.
Interaction of β-Aryl Di-N-acetylchitobiosides with Lysozyme
Authors: Otson R. , Reyes-Zamora C. , Tang J. Y. , Tsai C. S.
Published: December 2009

Nonproductive and productive interactions of lysozyme with some β-aryl di-N-acetylchitobiosides were studied. Difference ultraviolet and proton magnetic resonance spectroscopic methods were used to examine the nature and extent of nonproductive interactions. In the nonproductive binding mode, two glycose residues interact with subsites B and C. Information concerning productive interactions was deduced indirectly from rates of phenol liberation and from product analyses. The productive binding modes which place two glycose residues either at subsites C and D, or at subsites D and E, are consistent with experimental results. The contribution of the aryl aglycone to nonproductive and productive interactions suggests that there is flexibility of substrate specificity in lysozyme catalysis.
Paradoxical Inhibition of Phosphorylase by Pyridoxal Phosphate. III. Sequence of Amino Acids at Site of Reaction
Authors: Avramovic-Zikic O. , Welinder K. , Shechosky S. , Sodek J.
Published: December 2009

Pyridoxal phosphate phosphorylase b prepared from native phosphorylase b by the specific incorporation of 1–2 mol of pyridoxal phosphate (PLP) differs from the native enzyme in its absorbance, fluorescence, and kinetic properties. The secondary site of attachment of the PLP group responsible for these changes has been identified as a lysine residue from the formation of PLP-lysine on NaBH4 reduction. The peptide containing this derivative was isolated from a pepsin digest of the modified protein by Sephadex G-25 and Chromobeads type P resin column chromatography, followed by rechromatography on the resin after removal of the phosphate by alkaline phosphatase. The amino acid sequence of the purified hexapeptide was determined to be Tyr–(Pxy)Lys–Asn–Pro–Arg–Glu (Pxy, pyridoxyl). A second lysine reacting with PLP was found in the sequence Phe–Glu–Gly-(Pxy)Lys–Glu.
Inhibition of the Formation of Tetrahydroisoquinoline Alkaloids in Brain Homogenates
Authors: Alivisatos S. G. A. , Ungar Frieda , Callaghan Owen H. , Levitt LeRoy P. , Tabakoff Boris
Published: December 2009

The Pictet–Spengler condensation, involving interaction of properly activated aromatic compounds having an ethylamine side chain (e.g. dopamine) and aldehydes (e.g. acetaldehyde, aldehyde derivatives of biogenic amines, etc.), leads to the formation of tetrahydroisoquinoline derivatives like salsolinol or tetrahydropapaveroline. It may he arrested in the presence of compounds like ascorbate, cysteine, and glutathione. Cysteine is by far the most effective in preventing this condensation. The mechanism of inhibition is different with each agent: ascorbate and glutathione act either as reducing or complexing agents, while cysteine, which is the most effective of compounds studied so far, is a displacing agent and tends to form thiazolidine derivatives with various substituted aldehydes.
Determination of Cellulase Activity Using Hydroxyethylellulose as Substrate
Authors: Child J. J. , Eveleigh D. E. , Sieben A. S.
Published: December 2009

Nonionic celluloses are recommended to replace ionic celluloses as substrates in viscometric determinations of low levels of cellulase. A rapid, sensitive assay is described using hydroxyethylcellulose as substrate, and a correction factor is applied to compensate for deviations from linearity in viscosity measurement. The assay system has been used successfully for the measurement of low levels of extracellular and intracellular cellulases of both fungal and plant-cell origin.
Determination of Na+, K+, Mg2+, Cu2+, Zn2+, and Mn2+ in Rat Brain Regions
Authors: Donaldson J. , St. Pierre T. , Minnich J. L. , Barbeau A.
Published: December 2009

Na+, K+, Mg2+, Cu2+, Zn2+, and Mn2+ were determined in several regions of rat brain, using atomic absorption spectroscopy. Cu2+ was highest in the hypothalamus and lowest in the medulla oblongata. Zn2+ was also low in the medulla oblongata and highest in the hippocampal region. Mn2+ was found in high concentration in the hypothalamus.
Stimulation of Rat Liver Microsomal UDP-N-acetylglucosamine: Glycoprotein N-acetylglucosaminyltransferase by Carboxymethylcysteine-ribonuclease A
Authors: Letts Pamela J. , Schachter Harry
Published: December 2009

Carboxymethylcysteine-ribonuclease A (CMC-RNAase) stimulates the rat liver microsome-catalyzed transfer of N-acetylglucosamine from UDP-N-acetylglucosamine to protein. This effect is not due to incorporation of N-acetylglucosamine into an asparagine residue of CMC-RNAase but to stimulation of the transfer of N-acetylglucosamine into endogenous acceptor.
A Comparison of Inhibition Constants for the Inhibition of α-Lytic Protease and Porcine Elastase by Acetylated Alanine Peptides
Authors: Shaw M. C. , Whitaker D. R.
Published: December 2009

A comparison was made of the values of the inhibition constant Ki for the inhibition of α-lytic protease and porcine elastase by various N-acetylated L- and D-alanine peptides with N-benzoyl-L-alanine methyl ester as substrate for both enzymes. The Ki's for the inhibition of elastase by N-acetyl-L-alanine peptides decreased sharply as the degree of polymerization of the inhibitor increased, the respective values for monomer, dimer, and trimer being 1200 mM, 26 mM, and 2.7 mM. The corresponding estimates of Ki for α-lytic protease, viz. 310, 270, and 70 mM, showed comparatively little dependence on the degree of polymerization of the inhibitor and suggest a substantial difference in the binding sites of the two enzymes. The Ki's for inhibition of elastase by N-acetylated L-Ala-D-Ala, D-Ala-L-Ala, and D-Ala-D-Ala were, respectively, 55, 180, and > 300 mM; those for α-lytic protease were all > 300 mM.
Phospholipid Desaturation in Candida Lipolytica as a Function of Temperature and Growth
Authors: Kates M. , Paradis M.
Published: December 2009

Changes in the phospholipid fatty acids of a mesophilic yeast, Candida lipolytica, strain NRRLY 1094, were followed during growth at 10 °C or 25 °C. Total lipids were separated by thin-layer chromatography into phosphatidylcholine, phosphatidylinositol + phosphatidylserine, phosphatidylethanolamine, and neutral lipid fractions, and the fatty acids from each fraction were analyzed by gas–liquid chromatography. Unsaturation of all components was greater at 10 °C than at 25 °C, and was maintained at a higher level later into the active phase of growth at the lower temperature. A reciprocal relationship between percentages of oleic and linoleic acids during growth at either temperature was observed in all of the phospholipids, but was most pronounced in phosphatidylcholine. Positional distribution studies showed that desaturation during growth at either temperature occurred in fatty acids esterified both at the 1- and 2-positions of phosphatidylcholine, but specifically in the 2-position of phosphatidylethanolamine. Argentation chromatography indicated the existence in cells grown at either temperature of molecular species of lecithin containing four, three, two, and one double bonds. Calculations of the probable distribution of molecular species during growth suggest that desaturation of lecithin to a tetraenoic species occurs at both temperatures by stepwise desaturation of dienoic and trienoic molecular species. A similar pathway, with some modifications, is envisioned for phosphatidylethanolamine.
Structural Features Inhibiting the Cross-Reaction of the Acidic Polysaccharide from Tremella mesenterica with a Type II Anti-pneumococcal Serum
Authors: Fraser C. G. , Jennings H. J. , Moyna P.
Published: December 2009

The immunochemical behaviors of native, deacetylated, and periodate-oxidized acidic polysaccharides of Cryptococcus laurentii NRRL Y-1401 and Tremella mesenterica NRRL Y-6151 and Y-6158 were examined with type II anti-pneumococcal horse serum. Although the native and deacetylated polysaccharide of Cryptococcus cross-reacted, the equivalent Tremella polysaccharides did not. Smith degradations of the polysaccharides produced a reversal of this effect as the degraded polysaccharides of Tremella cross-reacted whereas that of Cryptococcus now failed to react. On the basis of this study it has now been established that the failure of the Tremella polysaccharides to cross-react with type II antiserum is due to steric interactions. The critical factor involved in the steric hindrance can be attributed to some strategically placed xylose units located in the vicinity of the glucuronic acid determinants. It has also been demonstrated that the periodate stability of the glucuronic acid residues of the Tremella polysaccharides is probably due to the presence of O-acetyl groups on the C-3 position of these residues.
Phenazine Methosulfate Uptake fey Rat Liver Mitochondria
Authors: French S. W. , Palmer D. S. , Sim W. A.
Published: December 2009

Calcium stimulated phenazine methosulfate (PMS) accumulation by rat liver mitochondria. PMS uptake required succinate, cyanide, and low O2 tension. The NADH-generating substrate β-hydroxybutyrate did not support PMS accumulation. The rate of PMS uptake was temperature dependent. Amytal, antimycin A, oligomycin, dinitrophenol, and malonate inhibited PMS uptake indicating that electron flow through the respiratory chain was involved. A 100% O2 atmosphere caused PMS efflux from mitochondria which had accumulated PMS anaerobically. It is postulated that PMS is sequestered in mitochondria as a precipitate when reduced by electron transfer. Nonenzymatic oxidation of PMSH by molecular oxygen solubilizes it and efflux from the mitochondria follows.
Fatty Acid Synthetase from Pythium debaryanum
Authors: Law Simon W. T. , Burton David N.
Published: December 2009

The presence of a fatty acid synthetase, capable of de novo synthesis of long chain fatty acids from acetyl-CoA, malonyl-CoA, and NADPH has been demonstrated in the simple fungus Pythium debaryanum (ATCC 9998), a member of the class Oomycetes. The enzyme is found in the supernatant fraction after centrifugation at 123 000 g for 35 min.The fatty acid synthetase was demonstrated to be of the multienzyme complex type, showing no dependence on acyl carrier protein for activity. The fatty acid products were identified as principally a mixture of free and esterified palmitic and stearic acids by gas-radiochromatography, and were shown to be synthesized de novo by the ratio of incorporation of acetyl- and malonyl-CoA, the Schmidt decarboxylation, and the lack of activity of medium and long chain acyl-CoA derivatives as acceptors of two carbon units in an elongation reaction. The pH optimum for the reaction was 6.8, and the Km for acetyl-CoA was 3.3 μM.The molecular weight of the fatty acid synthetase was estimated by gel filtration on Sepharose-4B as being of the order of 4 × 106. Attempts to reduce the apparent size of the enzyme by treatment with detergents and various enzymes were unsuccessful.
Studies on the Interchain Disulfides of Human Haptoglobins
Authors: Malchy B. , Dixon G. H.
Published: December 2009

Cyanogen bromide cleavages have been performed on the three major haptoglobin types in order to study the interchain disulfide linkages. Fragments (PC III's) were isolated which contained an intact haptoglobin α chain joined to a fragment of the haptoglobin β chain. Peptictryptic digests of the PC III fragment from Hp 1-1 confirmed the presence of the 21α-21α disulfide peptide and revealed the presence of disulfide peptides which contained half-cysteines 35α, 69α, 73α, and the half-cysteine present in the β chain fragment. The PC III fragments from the polymetric haptoglobins (2-1 and 2-2) were found to exist as a series of polymers. This indicated that the half-cysteine at position 21 in haptoglobin α1, which after the partial duplication results in half-cysteines at position 21 and 80 in α2, is responsible for the formation of the haptoglobin polymers.
Correction to the Amino Acid Sequence of the α Chain of Human Haptoglobin
Authors: Malchy B. , Dixon G. H.
Published: December 2009

The previously published amino acid sequence of the α chain of human haptoglobin must be corrected to include a half-cystine residue at position 73.
Transamination of Ring-Substituted L-Phenylalanines by an Extract from Rat Liver Mitochondria
Authors: Tong J. H. , Stoochnoff B. A. , D'Iorio A. , Benoiton N. Leo
Published: December 2009

The L- and D-isomers of m-tyrosine, o-tyrosine, p-chlorophenylalanine (p-CP), and p-fluorophenylalanine (p-FP) were tested as substrates for the soluble tyrosine aminotransferase and a mitochondrial extract of rat liver by measuring the amino acids formed with 2-oxoglutarate, oxaloacetate, and pyruvate as acceptors. None of the above were substrates for the soluble enzyme. L-m-Tyrosine, L-p-CP, and L-p-FP were transaminated at substantial rates (16–25% of the rate for L-tyrosine) by the mitochondrial enzyme with all three keto acids as amino group acceptors. A slow but definite transamination of L-o-tyrosine by the mitochondrial enzyme was demonstrated using labeled 2-oxoglutarate as acceptor.
Enzymatic and Physical Studies on the Triplex dTn∙dAn∙rUn
Authors: Murray Nancy L. , Morgan A. Richard
Published: December 2009

The triplex dTn∙dAn∙rUn was studied as a model system both enzymatically and physically with a view that a rational approach for attempting to isolate triplexes from in vivo situations might emerge. The triplex was characterized by mixing curves and by its equilibrium buoyant density. In 5 mM Na phosphate, pH 7.3, for KCl concentrations below 0.4 M the triplex dissociated into dTn∙dAn + rUn, dissociation being complete at about 0.3 M KCl. If MgCl2 replaced KCl a strongly cooperative dissociation occurred at 1 mM MgCl2. Whereas with alkaline titration of dTn∙dAn∙rUn, rUn was dissociated first followed by dTn∙dAn, acidic titration resulted in the whole triplex dissociating together. Both transcription and replication of dTn∙dAn were strongly inhibited by formation of a triplex. The DNA and RNA moieties in the triplex are somewhat protected against DNase I and pancreatic RNase degradation, when compared with duplex dTn∙dAn or rUn. Spermine binds equally well to dTn∙dAn and dTn∙dAn∙rUn which is consistent with spermine binding in the minor groove and RNA in the major groove of DNA.
The Mode of Action of 6-Methoxy-1,2,3,4-Tetrahydro-β-Carboline on Brain Serotonin
Authors: Ho Beng T. , Taylor Dorothy , Walker K. E. , McIsaac William M.
Published: December 2009

6-Methoxy-1,2,3,4-tetrahydro-β-carboline (6-MeO-THBC), which specifically elevates serotonin in the brain, exerted no significant effects on mouse brain monoamine oxidase, rat brain tryptophan hydroxylase, and rat liver tryptophan pyrrolase. There was a marked activation of rat plasma and liver 5-hydroxytryptophan decarboxylase and a concomitant increase of serotonin levels in the two tissues. 6-MeO-THBC did not alter the endogenous tryptophan levels in rat plasma and brain. A significant facilitation of the uptake of [3-14C]-5-hydroxytryptophan was observed in brains of mice treated with 6-MeO-THBC. The possibility that the increased serotonin was derived from 6-MeO-THBC itself was ruled out.
Tryptophan as a Source of One-Carbon Units for Purine Biosynthesis De Novo
Authors: Letter Anita A. , Zombor G. , Henderson J. Frank
Published: December 2009

Formate derived from the 2-position of the indole ring of tryptophan during the process of tryptophan catabolism via formylkynurenine and kynurenine has been shown to be utilized for purine biosynthesis de novo in mouse liver, kidney, and intestine. Hydrocortisone treatment both increases the rate of purine biosynthesis in liver and increases the rate of utilization of tryptophan for this process.
The Incorporation of Radioactivity from a Mixture of Selenium-75 and [methyl-3H]selenomethionines into selenomethylselenocysteine
Authors: Chow C. M. , Nigam S. N. , McConnell W. B.
Published: December 2009

Incorporation of radioactivity from L-[75Se]selenomethionine and DL-[methyl-3H]selenomethionine into selenomethylselenocysteine in Astragalus bisulcatus seedlings has been examined in mixed feeding experiments. About 60% more selenium-75 than tritium was incorporated into Se-methylselenocysteine. The results suggest independent incorporation of selenium and the methyl groups.
A Comparison of the Secretion of Two Components of Very Low Density Lipoproteins by Perfused Rat Liver
Authors: Kook Abraham I. , Rubinstein David
Published: December 2009

The synthesis and secretion by perfused rat liver of the lipid and protein moieties of the α- and β-lipoprotein-containing components of the very low density lipoproteins was studied, following additions of [3H]palmitate and [14C]leucine to the perfusate. The lipid moieties of both components became labelled early in the perfusion, and had a pattern of labelling similar to that of their protein moieties. The protein of the α-lipoprotein component became labelled at the same time as the lipid. The appearance of the isotope in the β-lipoprotein component was delayed, but it then surpassed that of the α-lipoprotein component in both total radioactivity and specific activity. From these data a working hypothesis has been developed which suggests that the protein but not the lipid of the β-lipoprotein component is incorporated into very low density lipoprotein in the sequence in which it is synthesized, while the α-lipoprotein component is drawn randomly from a large pool.
Motilin, a Gastric Motor Activity Stimulating Polypeptide: The Complete Amino Acid Sequence
Authors: Brown John C. , Cook Michael A. , Dryburgh Jill R.
Published: December 2009

Porcine motilin is a 22 amino acid residue polypeptide with the amino acid sequence Phe–Val–Pro–Ile–Phe–Thr–Tyr–Gly–Glu–Leu–Gln–Arg–Met–Glu–Glu–Lys–Glu–Arg–Asn–Lys–Gly–Gln. The calculated molecular weight is 2700.
Restoration by Fatty Acids of Active Transport in a Lactose Transport Mutant of Escherichia coli
Authors: Wong Paul T. S. , MacLennan David H.
Published: December 2009

A mutant of Escherichia coli ML 308-22 has lost its normal capacity to accumulate lactose analogues such as thiogalactosides without a reduction in the number and activity of the membrane carriers. The defect is only in the lactose transport system since transport of other sugars occurs at normal rates. Since the mutant was able to phosphorylate α-methylglucoside, the phosphotransferase system is believed to be fully operative. The addition of nucleotides, exogenous substrates, and surface active agents did not restore active galactoside transport in the mutant. However, the addition of extracts obtained from the wild type, ML 308, by osmotic shock or sonication enabled the mutant to accumulate up to 80% of the amount of galactoside accumulated by ML 308. The stimulating factor(s) in the shock fluid and cell-free extract was stable at 100° for 10 min and after proteinase treatment. A total lipid extract from ML 308 was partially stimulatory. When lipid classes were examined, phospholipids had little effect but free fatty acids were stimulatory. The stimulation of transport by fatty acids increased with increasing carbon-chain length to C18 and saturated fatty acids were found to be more stimulatory than unsaturated fatty acids. Addition of stearic acid at an optimal concentration of 0.2 mM caused an immediate increase in both the rate and the extent of [14C]thiomethylgalactoside ([14C]TMG) uptake in ML 308-22. Exit of [14C]TMG from the cell was slower in the presence of stearic acid. Growth of ML 308-22 in stearic acid medium had little effect on subsequent transport activity.
The Ribonuclease Activities of the Single-Strand-Specific Nucleases of Neurospora crassa
Authors: Tenenhouse H. , Fraser M. J.
Published: December 2009

A study of the ribonuclease activity of the single-strand-specific endonuclease of Neurospora crassa is reported. The enzyme degraded denatured, but not native, reovirus RNA. It had optimal activity with ribosomal RNA in the absence of added Mg2+ at pH 8.5 and was inhibited by ATP, mercaptoethanol, and EDTA. The inhibition by EDTA was overcome with Co2+ but not with Mg2+. The 5′-phosphoryl ends of the products of a partial digest comprised all four bases whereas 65% of the 3′-hydroxyl ends terminated with guanosine, indicating that the endonuclease had some base specificity. N. crassa endonuclease degraded purified yeast phenyl-alanine-specific tRNA (tRNAPhe) to large fragments with chain lengths of 13–14 nucleotides and to smaller fragments. This result indicated that the initial points of attack were the single-stranded "loop" regions of the tRNA molecule.Some new observations are also reported on the ribonuclease activity of single-strand-specific N. crassa exonuclease. In the presence of 10 mM Mg2+, the exonuclease removed the 3′-terminal AMP residue from tRNAPhe without "nicking" the molecule internally. When the concentration of Mg2+ was lowered to 1 mM, more extensive degradation of tRNA occurred.
Comparative Study of the Development of Alkaline Phosphodiesterase I and Alkaline Phosphatase in Mucosa of Rat Jejunem and Ileum
Authors: Hynie I. , Zbarsky S. H.
Published: December 2009

During the early postnatal period phosphodiesterase I is almost equally distributed in the jejunum and the ileum of rat intestine. By the end of the third week after birth the specific activity in the jejunum decreases to about one-half and in the ileum to about one-tenth of the activities found on the ninth day, forming a proximo–distal gradient typical of adult animals. The activity of alkaline phosphomonoesterase in newborns is much lower than that of phosphodiesterase I and increases rapidly the first day. During the second week the specific activity of alkaline phosphatase in the ileum rises to more than double that in the jejunum and the final proximo–distal gradient is established somewhat later. For both enzymes the amount of activity appearing as soluble cytoplasmic material is highest in newborn rats and diminishes as the animals mature. The extractibility of activity from the insoluble microsomal fractions with Triton X-100 follows the same trend. After extraction of the enzymes from microsomes by treatment with tert-amyl alcohol, Triton X-100, or glycerol, most of the phosphodiesterase I activity appears in large complexes of molecular weight of several millions, but after autolysis the complexes break down to molecules of molecular weight close to 150 000 without appreciable loss of activity.
Studies on Glycogen Metabolism in Normal and Diabetic Rat Heart In Vivo
Authors: Das Indrajit
Published: December 2009

A study has been made on the key enzymes involved in synthesis and breakdown of glycogen and the major intermediates in glycogen synthesis in isolated normal and streptozotocin diabetic rat heart. A significant loss of hexokinase isoenzyme type I and type II was observed in the soluble fraction of hearts from starved and diabetic rats.No significant change was observed in total and active form of glycogen synthetase and phosphorylase in diabetic rat heart, but glycogen synthetase phosphatase activity in vitro was found to be considerably less. Treatment with insulin restored the synthetase phosphatase in vitro activity, and also significantly increased synthetase I in vivo.Tissue content of the major intermediates on the glycogen synthetic pathway, glucose 6-phosphate, glucose 1-phosphate, and UDP-glucose, was found to be significantly higher in diabetic rat heart than in normal. Insulin (4 I.U./kg for 30 min) was able to normalize the high values of tissue content of the glycogen precursors found in diabetic heart. The decreased glycogen synthesis in diabetic rat heart seems to be mainly due to the decreased activity of glycogen synthetase phosphatase.
Dissociation Reassociation and Phenylalanine Incorporation by Chloroplast and Cytoplasmic Wheat-Leaf Ribosomes
Authors: Jones Berne L. , Nagabhushan N. , Tucker Edward B. , Zalik Saul
Published: December 2009

Ribosome preparations from wheat seedlings were separated by zonal centrifugation to yield monomers of 80 S (cytoplasmic) and 70 S (chloroplast). When centrifuged through gradients containing high KCl-to-MgCl2 buffer, the 80 S ribosomes dissociated into subunits of 61 S, 49 S, and 42 S, while the 70 S monomers gave subunits of 50 S and 30 S. After zonal separation of the subunits, they could be reassociated into parent ribosomes in the presence of MgCl2. Both 80 S and 70 S ribosomes actively synthesized polyphenylalanine in the presence of poly U. The rate of synthesis was similar for both species. Incorporation of phenylalanine by 80 S and 70 S ribosomes was inhibited by puromycin, was not inhibited by cycloheximide, and only the 70 S species was affected by chloramphenicol, indicating that the latter was of chloroplast origin.
Glucose Metabolism in an Isolated Blood Capillary Preparation
Authors: Rasio E. A.
Published: December 2009

Large amounts of blood capillaries consisting of vascular endothelium, pericytes, and interstitial collagen fibers can be prepared from the swimbladder of the common eel. This unique preparation has been employed to determine the glucose utilization by the capillary tissue in vitro. In a medium containing 5 mM glucose, the glucose uptake averages 25 μmol/g wet weight per hour. Most of the uptake is accounted for by aerobic glycolysis; the incorporation of glucose carbon into CO2, glycogen, total lipids, and proteins is quantitatively minor. All the glucose pathways are stimulated at various rates when the glucose concentration in the medium is raised from 5 to 30 mM. The addition of beef insulin to the medium does not modify glucose and alanine utilization. When capillaries are isolated from hyperglycemic alloxan-treated eels, the glucose uptake, lactic acid production, and glucose oxidation to CO2 compare with those of control capillaries and do not respond to fish insulin added in vitro. The results indicate that the rate of glucose utilization by isolated blood capillaries is not limited by the cell membrane permeability but depends, at least in part, on the glucose concentration in the extracellular medium.
Synthesis and Properties of δ-N-Hydroxyornithine
Authors: Tomlinson G. , Viswanatha T.
Published: December 2009

The chemical synthesis of the naturally occurring hydroxylamino acid, δ-N-hydroxyornithine, was attempted using a variety of experimental approaches. Only two such methods proved successful, both of which involved the partial reduction of a suitably protected nitro-derivative. The problems associated with the various procedures have been discussed.In aqueous solution at low pH, the compound was found to be moderately stable for periods of up to 1 week. The only detectable change was the slow spontaneous ring closure to the cyclic lactam, 1-hydroxy-3-amino-2-piperidone. Over longer periods, the presence of the oxidation product, the oxime of γ-glutamyl semialdehyde, became apparent. Slow hydrolysis of the latter resulted in the production of Δ1-pyrolline carboxylic acid. The rate of production of both these compounds was accelerated by raising the pH in the range 2,0–7.0. Above pH 7.0, the decomposition of δ-N-hydroxyornithine became rapid and complex, and was difficult to interpret. The oxidation of δ-N-hydroxyornithine to the oxime was found to be smoothly affected by ferricions. The effect of prolonged hydroysis with 6 N HC1 on δ-N-hydroxyornithine was to cause reduction to ornithine in good yield (> 65%). Only trace amounts of glutamic acid were noted. These observations suggest that disproportionation is not a major factor in the decomposition of δ-N-hydroxyornithine.
Reaction of Hydroxylamine Derivatives with Cinnamoylimidazole
Authors: Tomlinson G. , Gaudin J. E. , Viswanatha T.
Published: December 2009

The reaction of δ-N-hydroxyornithine with cinnamoylimidazole was found to involve a rapid acylation step followed by a slow deacylation of the acyl intermediate. The pH–rate profile of the reaction can be best explained on the basis of participation of the unprotonated hydroxylamine function of the amino acid in the reaction. The spectral properties of the acyl intermediate are consistent with it being an O-acyl derivative. A reexamination of the time-dependent increases in the reactivity of solutions of aminoxyalanine methyl ester revealed that the phenomenon could be correlated to the release of hydroxylamine. In contrast to these observations, no hydroxylamine release was noted in the solutions of canaline methyl ester and aminoxymethyl propionate and their reactivities remained unchanged with time.
Transient-Phase and Steady-State Kinetics for Enzyme Activation
Authors: Hijazi Nasrat H. , Laidler Keith J.
Published: December 2009

A non-steady-state analysis has been worked out for two mechanisms in which an activator Q can become attached to an enzyme–substrate complex EA, the species EAQ breaking down more rapidly than EA. It is shown that if EAQ breaks down into EQ + product there can be no steady state. If, however, EAQ breaks down into E + Q + product, the transient phase is followed by a steady state in which the product versus time curve is linear. A special case of this mechanism is when Q is the substrate (substrate activation). Some published kinetic data on carboxypeptidase are analyzed with reference to the equations derived.
Transient-Phase and Steady-State Kinetics for Inhibited Enzyme Systems. I. Single-Intermediate Mechanisms
Authors: Hijazi Nasrat H. , Laidler Keith J.
Published: December 2009

Equations for the pre-steady state and the steady state are derived for enzyme systems in which enzyme E, substrate A, and inhibitor Q are present, the enzyme concentration being lower than the substrate and inhibitor concentrations. It is assumed that the mechanism involves a single intermediate EA. Equations for competitive, anticompetitive, and pure noncompetitive inhibition are derived. When the inhibition is reversible the transient phase is followed by the establishment of a steady state. Analysis of experimental results is discussed for each type of inhibition. If the inhibition is irreversible, there is no steady state.
Transient-Phase and Steady-State Kinetics for Enzyme Systems Involving Two Substrates
Authors: Hijazi Nasrat H. , Laidler Keith J.
Published: December 2009

The transient-phase and steady-state equations are derived for four enzyme mechanisms involving two substrates, namely (1) Theorell–Chance mechanism, (2) ping pong bi bi mechanism, (3) ordered ternary-complex mechanism, and (4) random ternary-complex mechanism. In each case, a discussion is presented of the way in which the individual rate constants can be separated on the basis of experimental transient-phase investigations.
Effects of Exercise, Training, and Diet on Muscle Citric Acid Cycle Enzyme Activity
Authors: Dohm G. Lynis , Huston Richard L. , Askew E. Wayne , Fleshood H. Lee
Published: December 2009

The effects of training, exhaustive exercise, and diet on the activity of skeletal muscle citric acid cycle enzymes were studied. Training increased the activities of all cycle enzymes. Exhaustion of trained rats resulted in lowered activities of NAD-specific isocitrate dehydrogenase, succinate dehydrogenase, and cytochrome oxidase but citrate synthase and malate dehydrogenase were unaffected. The enzyme activities in untrained muscle were not changed by exhaustive exercise. High carbohydrate and high fat diets did not alter citric acid cycle activities in trained rested or untrained rested rats and did not moderate or accentuate the effects of exhaustive exercise. The results indicate that muscle citric acid cycle activity is increased by training and decreased by exhaustion of trained animals.
Chromatin Low Molecular Weight RNA Components
Authors: Monahan John J. , Hall Ross H.
Published: December 2009

A low molecular weight RNA fraction has been isolated from chromatin of L-cells, KB cells, DON Chinese hamster cells, and a rat hepatoma cell line. This RNA fraction has been further fractionated into 11 subfractions which have widely different polynucleotide chain lengths. All subfractions are present in each of the cell lines, though the relative proportions of each differ from one cell line to another. The base composition and approximate s value of the 11 individual L-cell subfractions were determined. It is possible that each subfraction contains multiple RNA components.
Translational Control of Protein Synthesis in Eat Anterior Pituitary by N-2′-O-dibutyryl adenosine 3′,5′-monophosphate
Authors: Boucher Roger , Gauthier Marie , Jolicoeur Paul , Labrie Fernand
Published: December 2009

Actinomycin D, at doses (25 and 50 μg/ml) that block RNA synthesis to less than 3% of the control rate, inhibits the incorporation of [3H]leucine into adenohypophyseal proteins and the release of newly synthesized proteins by 50 and 60%, respectively, of the control rates. Despite this lowering of basal levels of total protein synthesis and release in presence of the antibiotic, the percentage of stimulation of both protein synthesis and release by 5 mM N6-2′-O-dibutyryl adenosine 3′5′-monophosphate (dbcAMP) is not depressed by actinomycin D. When rat hemipituitaries are incubated with [3H]uridine, dbcAMP does not stimulate the labeling of total cytoplasmic RNA or the preferential labeling of any cytoplasmic RNA species resolved on sucrose gradient. There is no stimulatory effect of dbcAMP on total labeling or preferential incorporation into nuclear RNA species extracted at 24 °C or at 65 °C. Labeling of the nucleotide pools was unchanged up to 1 h of incubation but was increased (40–70%) during the last [Formula: see text] of incubation. These data suggest that the short-term stimulatory effects of dbcAMP on total adenohypophyseal protein synthesis and release are exerted at the transiational level.
Identification and Distribution of β-Phenylethylamine in the Rat
Authors: Durden D. A. , Philips S. R. , Boulton Alan A.
Published: December 2009

A procedure for the quantitative evaluation of some amines present in mammalian tissues has been developed. It includes isolation of the amines by ion exchange chromatography followed by conversion to dansyl derivatives, chromatographic separation, and quantitation by the mass spectrometric integrated ion current technique. The use of an isotopically labelled internal standard improves the precision and sensitivity of the analysis.The concentrations of β-phenylethylamine in some tissues of male Wistar rats were (ng/g); brain 1.8 ± 0.4, heart 5.7 ± 3.1, kidney 20.5 ± 2.2, liver 2.0 ± 0.7, lung 4.0 ± 1.4, and spleen 4.7 ± 2.7. In the brain the hypothalamus contained 25.3 ± 5.0, the cerebellum 3.4 ± 0.5, the stem 2.2 ± 0.9, the caudate nucleus 8.0 ± 0.3, and the 'rest' 1.1 ± 0.2 ng/g, respectively.
Lima Bean Protease Inhibitor: Reduction and Reoxidation of the Disulfide Bonds and Their Reactivity in the Trypsin–inhibitor Complex
Authors: Stevens Frits C. , Doskoch Elaine
Published: December 2009

Lima bean protease inhibitor is a protein which inhibits both trypsin and chymotrypsin at different and independent sites. Complete reduction of the disulfide bonds of the inhibitor results in loss of biological activity. By air oxidation of the reduced inhibitor, full chymotrypsin inhibitory activity and up to 50% of the trypsin inhibitory activity can be regained; the rates at which these activities are regained were different. Attempts to obtain selective cleavage of one or a few disulfide bonds by carefully controlling reaction conditions were unsuccessful. All the disulfide bonds of lima bean inhibitor appear equally accessible to the reagent and with a less than twofold molar excess of dithioerythritol over the molarity of disulfide bonds, complete reduction was obtained; both inhibitory activities were equally sensitive to reduction and were lost as a linear function of the average number of disulfide bonds reduced and carboxymethylated. In contrast to this, the disulfide bonds of lima bean inhibitor are stabilized when the inhibitor is in the form of a molar complex with trypsin. Under these conditions, only one out of a possible eight disulfide bonds could be reduced in the inhibitor with up to a 10-fold molar excess of dithioerythritol. The modified inhibitor obtained after dissociation of reduced and carboxymethylated trypsin–inhibitor complex appeared fully active against both trypsin and chymotrypsin.