bluuebunny/crossref_metadata_2025 huggingface dataset:
Microbiological degradation of bile acids. The preparation of some hypothetical metabolites involved in cholic acid degradation
Authors: Hayakawa S , Kanematsu Y , Fujiwara T , Kako H
Published: August 2015

1. To identify the intermediates involved in the degradation of cholic acid, the further degradation of (4R)-4-[4a-(2-carboxyethyl)-3aa-hexahydro-7ab-methyl-5-oxoindan-1β-yl]valeric acid (IVa) by Arthrobacter simplex was attempted. The organism could not utilize this acid but some hypothetical intermediate metabolities of compound (IVa) were prepared for later use as reference compounds. 2. The nor homologue (IIIa) and the dinor homologue (IIIb) of compound (IVa) were prepared by exposure of 3-oxo-24-nor-5β-cholan-23-oic acid (I) and (20S)-3b-hydroxy-5-pregnene-20-carboxylic acid (II) to A. simplex respectively. These compounds correspond to the respective metabolites produced by the shortening of the valeric acid side chain of compound (IVa) in a manner analogous to the conventional fatty acid a- and b-oxidation mechanisms. Their structures were confirmed by partial synthesis. 3. The following authentic samples of reduction products of the oxodicarboxylic acids (IIIa), (IIIb) and (IVa) were also synthesized as hypothetical metabolities: (4R)-4-[3aa-hexahydro-5a-hydroxy-4a-(3-hydroxypropyl)-7ab-methylindan-1b-yl]valeric acid (Vb) and its nor homologue (VIIa) and dinor homologue (IXa);(4R)-4-[3Aaa-hexahydro-5a-hydroxy-4a-(3-hydroxypropyl)-7ab-methylindan-1b-yl]-pentan-1-ol (Vc); and their respective 5β epimers (Ve), (VIIc), (IXc) and (Vf). 4. In connexion with the non-utilization of compound (IVa) by A. simplex, the possibility that not all the metabolites formed from cholic acid by a certain micro-organism can be utilized by the same organism is considered.
The effect of N-acylglucosamines on the biosynthesis and secretion of insulin in the rat
Authors: Ashcroft S J. H. , Crossley J R. , Crossley P C.
Published: August 2015

The effects of N-acylglucosamines on insulin release have been studied. N-Acylglucosamines stimulated insulin release from rat islets in vitro only if a sub-stimulatory concentration of glucose was also present, and this secretory response was abolished by mannoheptulose. In perifused islets the rapidity of the secreotry response to N-acetyl-D-glucosamine was similar to that observed with D-glucose. Increasing acyl-chain length from N-acetyl- to N-hexanoyl-D-glucosamine impaired the secretory response; however, N-dichloroacetyl-D-glucosamine was a more potent stimulator of release than was N-acetyl-D-glucosamine. Polymers of N-acetyl-D-glucosamine containing two to six monomers linked α1-4 did not stimulate insulin release; glucosamine linked to dextran via a propionyl or hexanoyl spacer group was also without insulin-releasing ability. N-Acylglucosamines were also effective in eliciting insulin release in vivo when injected into conscious rats. At the dose used (86 mumol), N-acetylgucosamine elicited a rapid rise in plasma-insulin concentration; N-butyrylglucosamine was less effective, and there was little or no response to N-hexanoylglucosamine. The response to N-dichloroacetyl-glucosamine was greater than that to N-acetylglucosamine; an increase in plasma insulin concentration could be elicited by N-dichloroacetylglucosamine at a dose (17 mumol) at which neither glucose nor N-acetylglucosamine was effective. The secretory response to acetylglucosamine is not mediated by conversion into glucose. Rates of (pro)-insulin biosynthesis by rat islets have been measured (Pro)-insulin biosynthesis was stimulated by glucose, and this response was abolished by mannoheptulose. N-Acetylglucosamine also stimulated (pro)-insulin biosynthesis; this effect of N-acetylglucosamine did not require the presence of glucose, and was not abolished by mannoheptulose. It is concluded that there are differences in signal reception and/or transduction for the processes of insulin biosynthesis and release.
Subunit composition and structure of subcomponent C1q of the first component of human complement
Authors: Reid K B M , Porter R R
Published: August 2015

1. Unreduced human subcomponent C1q was shown by electrophoresis on polyacrylamide gels run in the presence of sodium dodecyl sulphate to be composed of two types of non-covalently linked subunits of apparent mol.wts. 69 000 and 54 000. The ratio of the two subunits was markedly affected by the ionic strength of the applied sample. At a low ionic strength of applied sample, which gave the optimum value for the 54 000-apparent mol.wt. subunit, a ratio of 1.99:1.00 was obtained for the ratio of the 69 000-apparent mol.wt. subunit to the 5400-apparent-mol.wt. subunit. The amount of the 54 000-apparent-mol.wt. subunit detected in the expected position on the gel was found to be inversely proportional to increases in the ionic strength of the applled sample. 2. Human subcomponent C1q on reduction and alkylation, or oxidation, yields equimolar amounts of three chains designated A, B and C [Reid et al. (1972) Biochem. J. 130, 749-763]. The results obtained by Yonemasu & Stroud [(1972) Immunochemistry 9, 545-554], which showed that the 69 000-apparent-mol.wt. subunit was a disulphide-linked dimer of the A and B chains and that the 54 000-apparent-mol.wt. subunit was a disulphide-linked dimer of the C chain, were confirmed. 3. Gel filtration on Sephadex G-200 in 6.0M-guanidinium chloride showed that both types of unreduced subunit were eluted together as a single symmetrical peak of apparent mol.wt. 49 000-50 000 when globular proteins were used as markers. The molecular weights of the oxidized or reduced A, B and C chains have been shown previously to be very similar all being in the range 23 000-24 000 [Reid et al. (1972) Biochem. J. 130, 749-763; Reid (1974) Biochem. J. 141, 189-203]. 4. It is proposed that subcomponent C1q (mol.wt. 410000) is composed of nine non-covalently linked subunits, i.e. six A-B dimers and three C-C dimers. 5. A structure for subcomponent C1q is proposed and is based on the assumption that the collagen-like regions of 78 residues in each of the A, B and C chains are combined to form a triple-helical structure of the same type as is found in collagens.
Formation of angiotensin III by angiotensin-converting enzyme
Authors: Chiu A T , Ryan J W , Stewart J M , Dorer F E
Published: August 2015

Angiotensin III is formed from des-Asp1 -angiotensin I by angiotensin-converting enzyme. The Km (11 muM) of the reaction is one-third of that for the conversion of angiotensin I into angiotensin II. As suggested by the Km values, bradykinin, peptide BPP9a and angiotensins II and III are better inhibitors of the formation of angiotensin II than of the formation of angiotensin III.
Human lysosomal elastase. Catalytic and immunological properties
Authors: Starkey P M. , Barrett A J.
Published: August 2015

1. The elastase of human spleen was shown to exhibit endopeptidase activity against azo-casein and elastin. 2. Activity against several synthetic substrates was detected, and benzyloxycarbonyl-L-alanine 2-naphthyl ester was found to be a good substrate for routine use. 3. The enzyme showed a broad pH optimum in the range of 8.2-9.2 against azo-casein and the synthetic substrate. 4. The effect of inhibitors on the spleen elastase showed it to be a serine proteinase with a specificity similar to that of porcine pancreatic elastase. 5. Specific antisera were raised against the enzyme, and it was shown to be immunologically identical with the lysosomal elastase of human neutrophil leucocytes.
Polar-group behaviour in mixed monolayers of phospholipids and fusogenic lipids
Authors: Maggio B , Lucy J A.
Published: August 2015

1. The surface potentials of mixed monolayers of synthetic phospholipids with lipids that are fusogenic for hen erythrocytes were investigated. 2. At pH 5.6 and 10, but not at pH2, mixed monolayers of the fusogenic lipid, glycerol mono-oleate, with phosphatidylcholine exhibited negative deviations from the ideality rule in surface potential per molecule which were accompanied by negative deviations in mean molecular area. 3. Interactions of this type were not seen with chemically related but non-fusogenic lipids, nor were they found in mixed monolayers of any of the lipids with phosphatidylethanolamine. 4. Experiments with dihexadecyl phosphate and hexadecyltrimethyl-ammonium indicated that the complete head group of phosphatidylcholine is required for its observed behaviour with fusogenic lipids. 5. Bivalent cations (Ca2+, UO2(2+) or Zn2+) in the subphase at pH 5.6 significantly modified the behaviour of mixed monolayers of fusogenic lipids with phospholipids; there was a parallel perturbing effect of fusogenic lipids on interactions between monolayers of phospholipids and bivalent cations. 6. Possible molecular interactions of fusogenic lipids with membrane phospholipids, and the role of Ca2+, are discussed which may be relevant to cell fusion in erythrocytes induced by low-melting lipids in the presence of Ca2+.
Human placental diamine oxidase. Improved purification and characterization of a copper- and manganese-containing amine oxidase with novel substrate specificity
Authors: Crabbe M J , Waight R D , Bardsley W G , Barker R W , Kelly I D , Knowles P F
Published: August 2015

1. Isoelectric focusing studies of human placental diamine oxidase showed the pI value of the active enzyme to be 6.5. This information was used in modifying the enzyme purification by incorporating column chromatography on DEAE-Sephadex with ionic strength and pH gradient elution and this, together with affinity chromatography on concanavalin A-Sepharose, gave a highly purified preparation, with a specific activity of 7.0 units/mg. 2. The enzyme gave the expected stoicheiometry with p-dimethylaminomethylbenzylamine as substrate (Keq. 2700) and also oxidized [8-arginine]vasopressin, [8-lysine]vasopressin, collagen and tropocollagen. Polyacrylamide gel slices showed identical migration of diamine-oxidizing and [8-lysine]vasopressin-oxidizing activity. 3. The molecular weight, determined by ultracentrifugation, sodium dodecyl sulphate/polyacrylamide-gel electrophoresis, variable polyacrylamide-gel electrophoresis and Sephadex G-200 column chromatography, was estimated to be approx. 70000. 4. E.s.r. spectroscopy showed that copper and manganese were present in the purified enzyme. This result was confirmed by atomic absorption spectroscopy, which indicated a stoicheiometry for copper and manganese of approx. 1.0 and 1.2g-atom respectively/70000mol.wt. unit. 5. The e.s.r. spectral intensity did not decrease nor did the spectral line shape change when excess of p-dimethylaminomethylbenzylamine was added to the enzyme. 6. Addition of K13CN to the enzyme eliminated the copper e.s.r. signal without affecting the manganese signal. 7. The placental enzyme therefore appears to differ from other amine oxidases in terms of its metal cofactor requirement, molecular weight and substrate specificity, and possible roles in vivo for this enzyme are discussed.
Calcium uptake by subcellular fractions of pancreatic islets. Effects of nucleotides and theophylline
Authors: Sehilin J
Published: August 2015

Uptake of 45Ca2+ by a microsomal fraction isolated pancreatic islets of non-inbred ob/ob mice was studied. ATP strongly stimulated 45Ca2+ uptake, the maximum effect being obtained with 2mM-ATP. GTP and CTP at this concentration did not increase the uptake. Scatchard analysis revealed at least two types of uptake mechanisms in the presence of 2mM-ATP; the apparent association constants were 1.1 × 10(5)m(-1) and less than 2.5 × 10(2)m(-1). In contradistinction to an unaffected low-affinity uptake, the high-affinity uptake was drastically decreased on ommission of ATP. The ATP-dependent and high-affinity uptake was half-saturated at about 10-20mum-Ca(2+) and was inhibited by 10 or 100mum cyclic AMP, 10mum cyclic GMP, 10 mum cyclic GMP, or 5mm-theophylline. 45ca2+ uptake in the absence of ATP was not affected by 100mum-cyclic AMP. In view of its sensitivity to ATP and cyclic nucleotides, the high-affinity Ca2+-uptake mechaniam may play a role in stimulus-secretion coupling in the beta-cells by regulating the cytosolic concentration of Ca2+.
Effects of pronase and neuraminidase treatment on a myelin-associated glycoprotein in developing brain
Authors: Quarles R H
Published: August 2015

Rats (14 days old) were injected with [14c]fucose and young adult rats with [3H]fucose in order to label the myelin-associated glycoproteins. As previously reported, the major [14C]fucose-labelled glycoprotein in the immature myelin had a higher apparent molecular weight on sodium dodecyl sulphate/polyacrylamide gels that the [3H]fucose-labelled glycoprotein in mature myelin. This predominant doubly labelled glycoprotein component was partially purified by preparative gel electrophoresis and converted to glycopeptides by extensive Pronase digestion. Gel filtration on Sephadex G-50 separated the glycopeptides into several clases, which were designted A,B, C AND D, from high to low molecular weight. The 14C-labelled glycopeptides from immature myeline were enriched in the highest-molecular-weight class A relative to the 3H-labelled glycopeptides from mature myelin. Neuraminidase treatment of the glycoprotein before Pronase digestion greatly decreased the proportion of glycopeptides fractionating in the higher-molecular-weight classes and largely eliminated the developmental differences that were apparent by gel filtration. However, neuraminidase treatment did not decrease the magnitude of the developmental difference revealed by electrophoresing the intact glycoprotein on sodium dodecyl sulphate gels, although it did decrease the apparent molecular weight of the glycoprotein from both the 15-day-old and adult rats by an amount comparable in magnitude to that developmental difference. The results from gel filtration of glycopeptides indicate that there is a higher content of large molecular weight, sialic acid-rich oligosaccharide units in the glycoprotein of immature myelin. However, the higher apparent molecular weight for the glycoprotein from 15-day-old rats on sodium dodcyl sulphate gels is not due primarily to its higher sialic acid content.
The mechanism of the inhibition of the mitochondrial pyruvate transportater by α-cyanocinnamate derivatives
Authors: Halestrap A P
Published: August 2015

Pyruvate transport into rat liver mitochondria is inhibited by a variety of thiol reagents. alpha-Cyanocinnamate and its derivates, potent and reversible inhibitors of pyruvate transport, react reversibly with mercaptoethanol and cysteine to form addition products. It is concluded that these inhibitors react with an essential thiol group on the pyruvate carrier.
The subcellular loclization and properties of the ferrochelatase of etiolated barley
Authors: Little H N , Jones O T G
Published: August 2015

The etioplast fraction prepared from dark-grown barley contained the enzyme ferrochelatase. A mitochondrial fraction prepared from the same dark-grown tissue also contained ferrochelatase. After density-gradient centrifugation an etioplast band was collected that was free from detectable mitochondrial marker enzymes and yet retained ferrochelatase activity. A membrane band that was enriched in mitochondria also contained ferrochelatase. The ferrochelatase in these two bands had different pH optima, but appeared very similar in their porphyrin specificity and their inhibition by metalloporphyrins.
Deoxyribonucleoside triphosphate pools in vitamin B-12-deficient Euglenagracilis
Authors: Carell E F , Goetz G H
Published: August 2015

The size of the deoxyribonucleoside triphosphate pools of vitamin B-12-deficient cells of Euglena gracilis, and of vitamin B-12-deficient cells repleted with the vitamin, were measured. We found that the pools were very small, if they exist at all, in deficient cells but expand rapidly with the addition of the vitamin. The sizes of the pools decrease when DNA synthesis is completed, and are very small when the cells begin to divide.
Stimulation of peptide elongation by thyroxine
Authors: Carter W J , Faas F H , Wynn J O
Published: August 2015

This study suggests that thyroxine stimulates peptide elongation in a cell-free rat liver polyribosome system. The thyroxine effect persists in the presence of sufficient aurintricarboxylic acid to prevent polyuridylic acid-stimulated peptide initiation. In addition, thyroxine stimulates elongation of pre-existing polyphenylalanine chains providing conclusive evidence that the effect does not depend on peptide initiation. Thyroxine does not stimulate release of nascent peptides from ribosomes into the supernatant phase of the reaction mixture. Therefore in this protein-synthesis system the thyroxine effect is expected to occur at one or more of the reactions of peptide chain elongation, which include aminoacyl-tRNA binding, peptide bond synthesis and translocation.
Active-site determinations on forms of mammalian brain and eel acetylcholinesterase
Authors: Gordon M A , Chan S L , Trevor A J
Published: August 2015

Three forms of brain acetylcholinesterase were purified from bovine caudate-nucleus tissue and determined by calibrated gel filtration to have mol.wts. of approx. 120 000 (C), 230 000 (B) and 330 000 (A). [3H]Di-isopropyl phosphorofluoridate (isopropyl moiety labelled) was purified from commercial preparations and its concentration estimated by an enzyme-titration procedure. Brain acetylcholinesterase preparations and enzyme from eel electric tissue were allowed to react with [3H]di-isopropyl phosphorofluridate in phosphate buffer until enzyme activity was inhibited by 98%. Excess of [3H]di-isopropyl phosphorofluoridate that had not reacted was separated from the labelled enzyme protein by gel filtration, or by vacuum filtration or by extensive dialysis. The specificity of active-site labelling was confirmed by use of the enzyme reactivator, pyridine 2-aldoxime. The forms of brain acetylcholinesterase were calculted to contain approximately two (C) four (B) and six (A) active sites per molecule respectively. Acetylcholinesterase (mol.wt. 250 000) from electric-eel tissue was estimated to contain two active sites per molecule. Gradient-gel electrophoresis was used to confirm the estimation of molecular weights of brain acetylcholinesterase forms made by gel filtration. Under the conditions of electrophoresis acetylcholinesterase form A was stable, but form B was converted into a species of approx. 120 000 mol. wt. Similarly, form C of the brain enzyme was converted into a 60 000-mol.wt. form during electrophoresis. These results are in general accord with the suggestion that the multiple forms of brain acetylcholinesterase may be related to the aggregation of a single low-molecular-weight species.
Studies on the cholesterol ester hydrolase of Trogoderma (Coleoptera)
Authors: Agarwal H C , Nair A M G
Published: August 2015

The enzyme cholesterol ester hydrolase (EC 3.1.1.13) was detected in the larvae of the khapra beetle, Trogoderma granarium (Everts). The pH and temperature optima for the enzyme were 6.6 degrees and 37 degrees C respectively. The mol.wt. of the enzyme was 76000-80000. The enzyme was equally effective in hydrolysing cholesteryl acetate, stearate and oleate. Cholesterol derivatives, namely the chloride and the methyl ether, inhibited the enzyme activity almost completely. It was also inhibited completely by p-hydroxymercuribenzoate. This inhibition was reversed by the addition of dithiothreitol, reduced glutathione or cysteine. The enzyme activity was associated predominantly with the 104000 g fraction.
Dipeptidyl peptidase IV, a kidney brush-border serine peptidase
Authors: Kenny A J , Booth A G , George S G , Ingram J , Kershaw D , Wood E J , Young A R
Published: August 2015

Dipeptidyl peptidase IV, an enzyme that releases dipeptides from substrates with N-terminal sequences of the forms X-Pro-Y or X-Ala-Y, was purified 300-fold from pig kidney cortex. The kidney is the main source of the enzyme, where it is one of the major microvillus-membrane proteins. Several other tissues contained demonstrable activity against the usual assay substrate glycylproline 2-naphthylamide. In the small intestine this activity was greatly enriched in the microvillus fraction. In all tissues examined, the activity was extremely sensitive to inhibition by di-isopropyl phosphorofluoridate (Dip-F), but relatively resistant to inhibition by phenylmethylsulphonyl fluoride. It is a serine proteinase which may be covalently labelled with [32P]Dip-F, and is the only enzyme of this class in the microvillus membrane. The apparent subunit mol.wt. estimated by sodium dodecyl-sulphate/polyacrylamide-gel electrophoresis and by titration with [32P]Dip-F was 130 000. Gel-filtration and sedimentation-equilibrium methods gave values in the region of 280 000, which is consistent with a dimeric structure, a conclusion supported by electron micrographs of the purified enzyme. Among other well-characterized serine proteinases, this enzyme is unique in its membrane location and its large subunit size. Investigation of the mode of attack of the peptidase on oligopeptides revealed that it could hydrolyse certain N-blocked peptides, e.g. Z-Gly-Pro-Leu-Gly-Pro. In this respect it is acting as an endopeptidase and as such may merit reclassification and renaming as microvillus-membrane serine peptidase.
Iron-dependent binding of 8-anilinonaphthalene-1-sulphonate by both lactoferrin and transferrin
Authors: Bilić N , Casey M , Blanc B
Published: August 2015

Fluorescence of 8-anilinonaphthalene-1-sulphonate is enhanced by both lactoferrin and transferrin. The enhancement is relatively low between pH 4 and 8, and high at below pH 4. At physiological pH the fluorescence enhancement is higher with the iron-deprived than with the iron-saturated proteins. Binding of iron by lactoferrin is associated with lowering affinity for the dye.
Enzymes of 2-oxo acid degradation and biosynthesis in cell-free extracts of mixed rumen micro-organisms
Authors: Bush R S , Sauer F D
Published: August 2015

The enzymes of 2-oxo acid decarboxylation and 2-oxo acid synthesis (EC 1.2.7.1 and EC 1.2.7.2) were isolated and partially purified from cell-free extracts of rumen micro-organisms. The lyase was active with pyruvate, 3-hydroxypyruvate and 2-oxobutyrate. The synthase was active with acetate, 2-oxoglutarate or succinate. Pyruvate synthase was separated from pyruvate lyase by Sephadex G-200 gel filtration. With Sephadex filtration, approximate mol.wts. of 310000 and 210000 were determined for pyruvate lyase and pyruvate synthase respectively.
The identification and properties of phosphatases in skeletal muscle with activity towards the inhibitory subunit of troponin, and their relationship to other phosphoprotein phosphatases
Authors: Ray K P , England P J
Published: August 2015

1. Phosphoprotein phosphatases with activity towards the inhibitory subunit of troponin (troponin I), phosphorylase a and lysine-rich histone (fraction F1) have been fractionated from rat skeletal muscle by chromatography on Sephadex G-200 and polylysine-Sepharose. Six separate fractions were identified on the basis of substrate specificity and behaviour during chromatography. 2. All fractions showed similar Km values for any given protein substrate. The Km for troponin I (5 muM) was significantly lower than that previously reported. 3. Phosphatase activities towards troponin I and hosphorylase a did not show a requirement for bivalent-metal ions. Two of the fractions with only minor activity towards histone were activated by Mn2+. 4. Discontinuous polyacrylamide-gel-electrophoresis studies indicated that several of the fractions contained more than one phosphatase activity, and additionally showed that several of the activities could exist in different aggregation states. On the basis of these studies at least two phosphatases with activity only towards troponin I were identified. In addition, phosphorylase phosphatase (which has considerable activity towards troponin I) and a general phosphatase with activity towards all three substrates were found. 5. A fraction with mol.wt. of 150000 could be activated by freezing with 2-mercaptoethanol or by heating to 55 degrees C. This activation was accompanied by a decrease in mol.wt. to 25000. 6. The total amount of phosphatase with activity towards troponin I which was extracted would be sufficient to dephosphorylate all the troponin I present in skeletal muscle in approximately 10s.
The identification of 2,8-dihydroxyadenine, a new component of urinary stones
Authors: Simmonds H A , Van Acker K J , Cameron J S , Snedden W
Published: August 2015

Stones passed by a child homozygous for a deficiency of the enzyme adenine phosphoribosyltransferase have been identified by u.v., i.r. and mass spectrometry as 2,8-dihydroxyadenine.
Some properties of a soluble methane mono-oxygenase from Methylococcus capsulatus strain Bath
Authors: Colby J , Dalton H
Published: August 2015

Soluble extracts of Methylococcus capsulatus (Bath), obtained by centrifugation of crude extracts at 160000g for 1h, catalyse the NAD(P)H- and O2-dependent disappearance of bromomethane, and also the formation of methanol from methane. Soluble methane mono-oxygenase is not inhibited by chelating agents or by most electron-transport inhibitors, and is a multicomponent enzyme.
Characterization of upFc, a fragment of human immunoglobulin G1 produced by pepsin in urea
Authors: Parr D M , Hofmann T , Connell G E
Published: August 2015

The digestion of human IgG1/K myeloma proteins with pepsin in the presence of 8 M-urea produces fragments that differ from those produced by aqueous peptic digestion, and from other characteristic immunoglobulin fragments. Fb′2, the larger urea/pepsin fragment, was previously shown to consist of the constant regions of the light chains, and the CH1 domains and hinge regions of the heavy chains. The smaller fragment, upFc, has now been characterized. After reduction, three peptides were released from fragment upFc. Amino acid sequencing, N- and C-terminal determinations and amino acid compositions have enabled these peptides to be identified as residues Ile-253 to Leu-306, residues Thr-307 to Asp-376 and residues Thr-411 to Gly-446 of the heavy chain. Fragment upFc therefore contains the entire Fc region, beginning at residue Ile-253, except for a 34-residue section from within the CH3-domain disulphide loop. Peptic digestion of IgG1/K proteins in 8M-urea therefore provides a method for isolating from gamma1 heavy chains five homogeneous peptides in good yield, which account for almost the entire constant region. Characterization of fragments Fb′2 and upFc has shown that the action of pepsin in urea is entirely different from that of aqueous pepsin. Two gamma1 heavy chains have been shown to differ in sequence at three positions from the sequence reported for protein Eu.
The metabolic fate of intravenously injected peptide-bound chondroitin sulphate in the rat
Authors: Wood K M , Curtis C G , Powell G M , Wusteman F S
Published: August 2015

The degradation of intravenously administered chondroitin sulphate-peptide, obtained by trypsin digestion of rat cartilage preparations labelled in vitro with 35S (and, in some cases, with 3H), was studied in rats. As with free chains of chondroitin sulphate, the major site of accumulation and degradation in the body was the liver, although peptide-linked chains were taken up more rapidly than free chains. In the first 2h after intravenous injection of a chondroitin sulphate-peptide fraction, labelled macromolecular components were excreted in the urine. These were shown to be chondroitin sulphate-peptide of the same degree of sulphation but of smaller average size than the injected material. A similar observation was made when free chains of chondroitin sulphate from the same source were administered intravenously. An isolated perfused rat kidney failed to de-sulphate circulating chondroitin sulphate-peptide, but a component of lower average molecular weight was excreted in the urine. When a chondroitin sulphate-peptide fraction of relatively larger hydrodynamic volume was administered, very little chondroitin sulphate appeared in the urine in the first 2h. It was concluded that, depending on size and/or peptide content, the chondroitin sulphate-peptide released from connective tissues into the circulation would probably be subjected to one of two alternative fates. The smaller fragments are more likely to be excreted in the urine, whereas the larger ones are taken up by the liver and there degraded to inorganic sulphate and undefined carbohydrate components.
Oxidation of cholesterol and cholesterol analogues by mitochondrial preparations of steroid-hormone-producing tissue
Authors: Arthur J R , Blair H A F , Boyd G S , Mason J I , Suckling K E
Published: August 2015

The rate of oxidation of cholesterol and its analogues to pregnenolone (3beta-hydroxypregn-5-en-20-one) by various mitochondrial preparations was measured. Sterols with the cholest-5-en-3beta-ol ring system and saturated side chains of different lengths were converted into pregnenolone rat rates similar to that of cholesterol. This marked lack of mitochondrial specificity towards the steroid side chains is in direct contrast with the rat liver microsomal cholesterol 7alpha-hydroxylase, which has a high specificity for the side chain. Steroids that retain the ring system, but contain hydroxyl groups at various points in the side chain, are converted into pregnenolone at rates three to eight times higher than in cholesterol. The results are discussed with reference to current ideas on the mechanism of the side-chain cleavage of cholesterol. The results are discussed with reference to current ideas on the mechanism of the side-chain cleavage of cholesterol.
The properties of the primary electron acceptor in the Photosystem I reaction centre of spinach chloroplasts and its interaction with P700 and the bound ferredoxin in various oxidation-reduction states
Authors: Evans M C W , Sihra C K , Cammack R
Published: August 2015

The properties of the component ‘X’ identified as the primary electron acceptor of Photosystem I in spinach was investigated by electron-paramagnetic-resonance spectroscopy and the complete spectrum obtained for the first time. Component ‘X’ has gx = 1.78, gy = 1.88 and gz = 2.08; it can be observed only at very low temperatures (8-13K) and high microwave powers. Component X was identified in Photosystem I particles prepared with the French press or with Triton X-100. In samples reduced with ascorbate, illumination at low temperatures results in the photo-oxidation of P700 and reduction of a bound iron-sulphur protein; this is irreversible at low temperature. In samples in which the iron-sulphur proteins are reduced by sodium dithionite, illumination at low temperature results in the oxidation of P700 and the reduction of component ‘X’; this is reversible at low temperature. The light-induced P700 signal is the same size with either ascorbate or dithionite as reducing agent, showing that all of the P700 involved in reduction of bound ferredoxin also functions in the reduction of component ‘X’.
Anti-ketogenic effect of glucose in the lactating cow deprived of food
Authors: Treacher R J , Baird G D , Young J L
Published: August 2015

1. The aim of this study was to determine the effect of a constant infusion of glucose on the ketosis that is observed when dairy cows are deprived of food in early lactation. 2. Cows in early lactation were first deprived of food for 4 days (96h) to induce a ‘fasting ketosis’. Glucose was then infused intravenously at a constant rate of 0.75 g/min for 48h while deprivation of food was maintained. At the end of this 48 h period, blood and liver ketone-body concentrations had decreased to values well below those found in healthy fed cows. 3. On the assumption that the anti-ketogenic effect of glucose was mainly due to suppression of hepatic ketogenesis, it was concluded that two anti-ketogenic mechanisms had been identified. These were (a) a decrease in the availability of free fatty acids for hepatic oxidation, and (b) anti-ketogenic changes within the liver itself. 4. These latter anti-ketogenic changes were twofold. The first was a major increase in the hepatic concentrations of citrate and 2-oxoglutarate. The second was an increase in the degree of oxidation of the hepatic cytosol. It was proposed that both these intrahepatic changes might indicate an augmentation of the quantity of oxaloacetate available for condensation with acetyl-CoA derived from fat oxidation. 5. Hepatic glycerol 1-phosphate concentration fell substantially after glucose infusion. 6. Glucose infusion into fed cows produced qualitatively similar effects to those observed in the unfed cows. However, blood and liver ketone-body concentrations were not decreased to the same extent in the fed cows as in the unfed cows.
The metabolism and binding of catecholamines by the hepatic microsomal mixed-function oxidase of the rat
Authors: McKillop D , Powis G
Published: August 2015

Noradrenaline and adrenaline were metabolized by an NADPH- and oxygen-dependent process located within the hepatic microsomal fraction of the rat. Metabolism was inhibited by CO and compound SKF 525A, but not by pargyline, an inhibitor of monoamine oxidase, or by 3,4-dimethoxy-5-hydroxybenzoic acid, an inhibitor of catechol O-methyltransferase. It is concluded that the enzyme system responsible for the metabolism of the catecholamines was the microsomal mixed-function oxidase. The Km for noradrenaline was 2.4 mM and for adrenaline 1.0 mM, and V 15.6 and 3.6 nmol/min per mg of microsomal protein respectively. Both catecholamines bound to the microsomal fraction, producing a type II spectral change, with a Ks for noradrenaline of 0.9 mM and for adrenaline of 1.0 mM, and showed other characteristics of type II compounds by inhibited the reduction of cytochrome P-450 by NADPH and exhibiting an enhanced metabolism in the presence of acetone. The major product of catecholamine metabolism was an as yet unidentified alkali-labile compound, which did not correspond to any of the recognized catecholamine metabolites.
Uptake of mevalonate and acetate during plastid development
Authors: Wellburn A R , Hampp R
Published: August 2015

1. The envelopes of etioplasts and 1-2h etiochloroplasts are permeable to mevalonate, but plastids from etiolated tissue illuminated for longer than 4h show progressive impermeability towards mevalonate. 2. Acetate permeates the envelopes of 1-4h etiochloroplasts but does not significantly cross the envelopes of etioplasts or 8-24h etiochloroplasts. 3. A translocator system exists within the plastid envelopes for mevalonate which relies on malate as a counter-exchange anion.
The pre-eminence of kcat. in the manifestation of optimal enzymic activity delineated by using the Briggs-Haldane two-step irreversible kinetic model
Authors: Brocklehurst K , Cornish-Bowden A
Published: August 2015

The suggestion by Fersht [(1974) Proc. R. Soc. London Ser. B 187, 397-407] that enzymes that provide maximal rates of catalysis should be characterized by values of Ks, the dissociation constant of the enzyme-substrate complex, greater than 10 times the value of the ambient substrate concentration has been examined. 2. For such enzymes, Ks is not relevant, and attention is best focused on the relative numerical values of k(cat). (in units of s(-1) and the substrate molarity. It is necessary only that the former be about 10(10)-10(11) times the latter to ensure that the rate of product formation be diffusion-limited and thus maximal.
The proton and metal complexes of adenyl-5′-yl imidodiphosphate
Authors: Pettit L D , Siddiqui K F
Published: August 2015

The formation constants of the complexes of adenyl-5′-yl imidodiphosphate with H+ Mg2+, Ca2+ and a number of bivalent transition-metal ions were measured potentionmetrically. The complexes are generally a little more stable than the analogous complexes of ATP. By measuring the formation constants at two temperatures, this increase in stability was shown to result from an increased enthalpy change on complex-formation.
The construction and analysis of sucrose gradients for use with zonal rotors
Authors: Hirst W , Cox R A
Published: August 2015

The rate of sedimentation of a particle in a sucrose solution depends on the viscosity and density of the medium. These two variables are related to the sucrose concentration and the temperature of the medium by new simple equations. These equations were used in a rapid iterative procedure that relates the distance moved by a zone in a continuous sucrose gradient to its sedimentation coefficient. It is shown by comparison with experiment that this iterative method allows the distance moved by a zone to be calculated rapidly. The method may therefore be used to optimize the separation of particles in a sucrose-gradient-centrifugation experiment. The method also allows the unknown sedimentation coefficients of several zones to be measured from a single sucrose-gradient-centrifugation experiment.
Stable thiobarbituric acid chromophore with dimethyl sulphoxide. Application to sialic acid assay in analytical de-O-acetylation
Authors: Skoza L , Mohos S
Published: August 2015

With dimethyl sulphoxide instead of butanol in the thiobarbituric acid assay for sialic acid, a non-fading chromophore with lambdamax. = 549 nm was produced in a homogeneous solution, allowing dilution of the test mixture in case of high colour yield. This test adapted well to studies on alkaline de-O-acetylation. Bovine and rat submaxillary mucins, and rabbit Tamm-Horsfall urinary sialoproteins contain O-acetyl isomers of neuramine acid that are resistant to the thiobarbituric acid assay. Alkaline de-O-acetylation converted resistant O-acetylneuraminic acid into thiobarbituric acid-reactive sialic acid, and such conversion paralleled de-O-acetylation as measured by the ferric hydroxamate method. The colour increment was similar when the alkaline treatment of bovine submaxillary mucin either preceded or followed the acid hydrolysis. Only alkaline preptreatment was effective with rat submaxillary mucin. By selecting optimal conditions for alkaline de-O-acetylation, O-acetyl isomers can be accurately assessed by the thiobarbituric acid assay.
Purification and chemical characterization of human hexosaminidases A and B
Authors: Lee J E S. , Yoshida A
Published: August 2015

N-Acetyl-β-hexosaminidases A and B were purified to homogeneity from human placenta. In the initial step of purification, the enzymes were adsorbed on concanavalin A-Sepharose 4B and eluted from the column with α-methyl D-mannosides. Subsequent purification steps included DEAE-cellulose column chromatography, QAE-Sephadex [diethyl-(2-hydroxypropyl)aminoethyl-Sephadex] column chromatography, Sephadex G-200 gel filtration and preparative disc polyacrylamide-gel electrophoresis, followed by another QAE-Sephadex chromatography for the hexosaminidase A preparation, and DEAE-cellulose column chromatography, calcium phosphate gel chromatography, Sephadex G-200 gel filtration, QAE-Sephadex chromatography and CM-cellulose chromatography for the hexosaminidase B preparation. The purified preparations, particularly hexosaminidase A, had significantly higher specific enzyme activities than previously reported. The preparations moved on polyacrylamide-gel electrophoresis as single protein bands, which also stained for enzyme activity. Sedimentation-equilibrium centrifugation indicated homogenous dispersion of the enzymes, and the molecular weight was estimated as about 110000 for both enzymes. Complete amino acid and carbohydrate compositions of the two isoenzymes were determined, and, in contrast with previous suggestions, no sialic acid was found in the enzymes.
The subunits of human hexosaminidase A
Authors: Beutler E , Yoshida A , Kuhl W , Lee J E S.
Published: August 2015

Previous studies of the subunit structure of hexosaminidase gave ambiguous results, but suggested that the enzyme was composed of six equally sized subunits. Dissociation of hexosaminidase A with p-chloromercuribenzoate produces an alkylated fragment with mol.wt. approx. 50000, which is converted into hexosaminidase S by treatment with dithiothreitol. Treatment of native hexosaminidase A with sodium dodecylsulphate results in the formation of a large and a small fragment. However, although the native enzyme has a sedimentation coefficient of 5.8S, dissociation by S-carboxymethylation and maleic anhydride treatment results in subunits exhibiting a single schlieren boundary on analytical ultracentrifugation with a sedimentation coefficient of 2.18S. These results indicate that the enzyme is composed of four subunits, each with molwt. approx. 25000-27000. The mol.wt. of the native enzymes is calculated to be approx. 110000. Our data are consistent with the subunit structures of hexosaminidases A, B and S as being α2β2, β4 and α4 respectively.
The α macroglobulins of rat serum
Authors: Gordon A H
Published: August 2015

A three-stage method for isolation of α1 macroglobulin and α2 macroglobulin from the serum of normal and injured rats is described. The methods successively used, namely gel filtration, ultracentrifugation and chromatography on DEAE-cellulose, were chosen to minimize loss of tryptic esterase-protecting activity. The two proteins differed slightly with respect to the following properties: mol.wt., α1 macroglobulin 7.46 × 10(5), α2 macroglobulin 7.16 × 10(5); isoelectric focusing, α1, macroglobulin pI 4.4, α2 macroglobulin pI4.5. Amino acid analyses were identical, except with respect to tyrosine: α1 macroglobulin 3.96 ± 0.24, α2 macroglobulin 3.16 ± 0.32 mol/100 mol of total amino acids. When isolated from the serum of uninjured rats, α1 macroglobulin retained the capacity to bind 1.05 mol of trypsin/mol. However, if isolated from serum 2 days after injury only 0.78 mol of trypsin/mol of α1 macroglobulin was bound. α2 macroglobulin isolated from this latter serum bound on average 0.97 mol of trypsin/mol. When reduced with N-acetylcysteine, both molecules formed subunits of size corresponding to that expected for quarter molecules. When α2 macroglobulin was reduced with dithiothreitol, quarter molecules were again produced. α1 macroglobulin, however, when thus treated gave a more complex mixture, containing a component having a mol.wt. of less than 6 × 10(4). Antisera raised against the two proteins permitted estimation of the concentration of each protein in the plasmas or sera of normal and injured rats. Plasma from normal male rats contained 3.76 ± 0.56 mg of α1 macroglobulin/ml (n = 33) and 0.016 ± 0.001 mg of α2 macroglobulin/ml (n=33). After injury by injection of turpentine and cortisone, the concentrations in plasma were at 3 days 5.19 ± 0.81 mg of α1 macroglobulin/ml (n = 12) and at 2 days 1.38 ± 0.35 mg of α2 macroglobulin/ml (n = 12). Antisera to the two proteins did not cross-react with one another. The quarter molecules formed by reduction of both proteins showed increased antigenicity.
Uptake of iodinated human kidney α-D-mannosidase by rat liver- Association with membrane elements and stability in vivo and in vitro
Authors: Marinković D V , Petrović S L , Martinović J V , Marinković J N
Published: August 2015

1. Human kidney α-D-mannosidase (form A) was labelled with 125I to a specific radio-activity of approx. 2250muCi/mg of protein, essentially without loss of enzymic activity. The enzymic activity and radioactivity of the iodinated material also co-migrated in gel filtration and gel electrophoresis. 2. The binding of 125I-labelled mannosidase in vitro to particulate material in liver and kidney homogenates was of the other of 2 pg/mg of particulate material in liver and kidney homogenates was of the order of 2pg/mg of particulate protein withing 16h at 37 degrees C, and essentially zero in intervals of up to 60 min. The degradation in vitro of labelled exogenous mannosidase was of the order of 10-20pg/ 16th per mg of protein in postnuclear supernatant, and it was saturated entirely within 1h at 37 degrees C. 3. The binding of labelled mannosidase in vivo to particulate elements of liver homogenates 60 min after intravenous injection was at least 10 times higher in terms of specific radioactivity than the highest value attainable in vitro. Virtually all exogenous enzyme bound to liver particulate material could be recovered in macromolecular form after disruption of membranes by detergents. 4. The radioactive enzyme bound to liver particulate material could be detached almost completely by shearing, repeated freezing and thawing, and exposure to strong detergents under conditions that do not eliminate rough-endoplasmic-membrane structure. It could bot be released, however, by high salt concentration (0.5M-KC1) or by exposure to weak detergents such as Tween 80. The particle-bound enzyme should thus be associated with plasma membranes and lysosome-like elements. 5. Of the rat tissues studied, only liver could approach, within 60 min after the injection, the concentration of exogenous mannosidase found in the blood serum. The activity per g tissue weight fell progressively from liver (60% of serum value) to kidney (16% of serum value), lung (8% of serum vlaue), spleen (6% of serum value) and brain (0.9% of serum value). Most of the radioactive enzyme found in tissues other than liver appeared to be present in a free form, whereas in liver more than 50% of the labelled enzyme was associated with membrane elements.
The instantaneous monitoring of polyacrylamide gels during electrophoresis
Authors: Elliott A
Published: August 2015

The advantages of being able to see protein zones in a gel during electrophoresis (and hence before staining) are pointed out, and a method is described which depends on local increments of refractive index in these zones. The use of local increments of refractive index in polyacrylamide gels for measuring protein concentrations in zones during electrophoresis is briefly considered; it is found that such increments are greater than would be expected from the amount of protein when sodium dodecyl sulphate is present. The enhancement depends on conditions and time of running. This makes quantitative estimates difficult, but the sensitivity of detection of protein zones by observations based on refractive-index changes is greatly increased by this property of sodium dodecyl sulphate. Methods are described for making optically uniform gels (both with uniform and with graded concentrations of polyacrylamide), necessary for observation of small changes in refractive index. A simple dark-field system of observation is described. Examples are given showing protein samples observed with the system during electrophoresis and compared with the same gel stained with Coomassie Blue after completion of the run. Under optimal conditions the optical method is comparable in sensitivity with staining. With the proteins of lower mol.wt. (approx. 15000), the optical method is not so sensitive, becoming less sensitive with longer running time. This loss of sensitivity is greatly decreased by using more concentrated polyacrylamide gels, and graded gels are therefore more suitable for optical observation than are uniform gels. The observation of protein zones during electrophoresis adds nothing to the time needed for making a stained gel and gives much information long before it can be obtained from the stained gel.