Canadian Science Publishing
0008-4018
Cơ quản chủ quản: N/A
Lĩnh vực:
Các bài báo tiêu biểu
Purification and Properties of Rat Liver Nuclear Protein Kinases Two protein kinases, designated NI and NII, have been isolated from rat liver nuclei. These enzymes have a similar pH optimum and phosphorylate phosvitin and casein more readily than histone. Both enzymes require magnesium for activity. In the absence of Mg2+ , other divalent cations such as Ca2+ , Co2+ , and Mn2+ can substitute partially for Mg2+ when the reaction is catalyzed by NI. With NII, only Co2+ showed any activity in the absence of Mg2+ . Magnesium decreased the apparent Km for ATP of protein kinase NI without changing the Vmax of the reaction, and decreased the apparent Km 's for both ATP and casein, while increasing the Vmax of the reaction threefold with protein kinase NII. Both enzymes are stimulated about twofold by low concentrations (0.1–0.3 M) of NaCl, KCl, and sodium acetate, whereas higher concentrations (> 0.5 M) inhibit their activities. Both enzymes are inhibited by low concentrations of NaF (0.02 M) and (NH4 )2 SO4 (0.1 M). NI and NII were found to have sedimentation coefficients of 3.6 S and 10.8 S, respectively. The nuclear protein kinases are not activated by cyclic AMP or cyclic GMP, and are not inhibited by the heat-stable cyclic AMP-dependent protein kinase inhibitor.
Tập 50 Số 12 - Trang 1249-1259 - 1972
THE COMPOSITIONS OF SOME PEPTIDES PRODUCED BY AN ENZYMIC HYDROLYSIS OF WHEAT GLIADIN Wheat gliadin was hydrolyzed extensively by treatment with pepsin and then by trypsin. A large number of peptides were produced as well as small amounts of some amino acids, thus indicating a substantial amount of hydrolysis of gliadin by the enzymes. Five peptides were obtained crystalline and two of these constitute 11.5% and 1.2% of gliadin, respectively. Their structures have been partly determined. The results indicate that wheat gliadin contains (Asp.Asp) bonds and at least 1.9% of the glutamic acid is present as glutamylglutamic acid.
Tập 42 Số 8 - Trang 1133-1140 - 1964
A rapid method for the purification of antibody–enzyme conjugates A method is described for a rapid and efficient separation of enzyme-labelled antibodies from the free enzyme following the coupling reaction. A single passage of the reaction mixture on a protein A – Sepharose CL-4B column gave a sharp separation of the free enzyme from the conjugate.
Tập 57 Số 3 - Trang 286-288 - 1979
The Control of Pyruvate Kinases of <i>Escherichia coli</i>. II. Effectors and Regulatory Properties of the Enzyme Activated by Ribose 5-Phosphate The pyruvate kinases of Escherichia coli activated by ribose 5-phosphate (RP) has been partially purified. The active form of the enzyme has a molecular weight of about 180 000 as judged by sucrose density gradient centrifugations and Sephadex G-150 chromatography. On dissociation in the absence of sulfhydryl reagents such as dithiothreitol, the enzyme is inactivated and it has a molecular weight of about 110 000. Various substrates and effectors of the enzyme, with the exception of phosphate, do not influence the association–dissociation equilibrium of the enzyme.The enzyme, unlike pyruvate kinases from many other sources, is not activated by potassium ions. Sulfate and phosphate ions are inhibitory to the enzyme. Phosphate seems to be an allosteric inhibitor and its effect is completely antagonized by activators. The enzyme is activated in an allosteric manner by two classes of compounds, nucleoside monophosphates and sugar phosphates of the hexose monophosphate pathway. Amongst the nucleotides, guanosine 5′-phosphate and adenosine 5′-phosphate are the most effective activators. Amongst the hexose monophosphate pathway intermediates, RP is the most powerful activator, with apparent activation constants as low as 1 μM. Sugar phosphates esterified at C-1 or both terminal positions are entirely ineffective in activation. The effectors act by changing the Michaelis constant for the substrates. Both of the substrates of the enzyme, adenosine diphosphate and phosphoenolpyruvate, yield cooperative rate–concentration plots in the presence of unsaturating concentrations of the fixed changing substrate. The initial velocity plots for both substrates become hyperbolic in the presence of saturating concentrations of RP.
Tập 53 Số 4 - Trang 444-454 - 1975
THE EFFECT OF LIPID MICELLES ON MITOCHONDRIAL MALATE DEHYDROGENASE Mitochondrial malate dehydrogenase (M-MDH) is known to be very unstable in aqueous solution. This instability may be ascribed to removal of the enzyme by severe extraction procedures from its bound state in the mitochondrion.Whole heart lipid micelles, mitochondrial lipids, and fatty acids increase the stability of the enzyme. The degree of lipid ability to increase activity of M-MDH is dependent on the ionic character of the environment. Thus the enzyme exhibits higher activity in a lipid–phosphate system than in lipid–Tris–acetate or lipid–KCl. Likewise, the enzymatic activity is higher in lipid than in non-lipid media. The relative ability of lipid to stimulate M-MDH activity is independent of pH, ionic strength, and temperature (between 6 and 37 °C). Preliminary evidence suggests that lipid acts by altering the conformation of the tertiary structure of the enzyme.The results, in general, suggest that hydrophobic-group interactions increase enzyme stability. These interactions may, in part, simulate the actual type of binding which stabilizes the enzyme activity in vivo.
Tập 45 Số 6 - Trang 839-851 - 1967
MULTIPLE FORMS OF LACTATE DEHYDROGENASE AND ASPARTATE AMINOTRANSFERASE IN HERRING (CLUPEA HARENGUS HARENGUS L.) The distribution of isoenzymes of lactate dehydrogenase (LDH) and aspartate aminotransferase (AAT) in the tissues of 189 herring (Clupea harengus harengus L.) were examined. Starch-gel electrophoresis of the LDH isoenzymes of the herring revealed the presence of two hybrid forms representing mutant alleles at the B locus. These mutants gave rise to two genotypes, BB′ and BB″, whose LDH staining patterns revealed a binomial distribution of the tetramer combinations formed from a free and random association of the A, B, and B′, and the A, B, and B″ monomers respectively.A hybrid form of soluble AAT was found. Its electrophoretic pattern showed a 1:2:1 binomial distribution of bands. It is postulated that these bands represent AAT dimers formed from normal S and mutant S′ monomers of a heterozygous SS′ genotype. The normal homozygous SS genotype showed only one band of activity.The normal levels of LDH and AAT activity in plasma and in heart and skeletal muscles were determined. During frozen storage LDH-5 activity gradually disappeared, while LDH-1 activity changed least; LDH-1 was also most stable at higher temperatures. Frozen storage rapidly destroyed AAT activity.
Tập 44 Số 10 - Trang 1319-1326 - 1966
A Spin Label Study of the Influence of Cholesterol on Egg Lecithin Multibilayers A detailed electron spin resonance study of a cholestane spin label in hydrated egg lecithin multibilayers of variable cholesterol content is presented. Several theoretical models are proposed in an attempt to explain the observed electron spin resonance spectra for the egg lecithin–cholesterol multibilayer system; we conclude that the most probable model is that of restricted random walk of individual spin labels where the amplitude of the random walk decreases from about 46° at 0 mol% cholesterol content to a minimum of 17° at 55 mol% cholesterol. Also, as the cholesterol content of the multibilayers increases, so the rate of random walk decreases from rapid to intermediate on the electron spin resonance time scale. The results clearly indicate that cholesterol is able to order egg lecithin films, orientating all molecules towards a normal to the surface of the film and decreasing their mobility. The condensing and stiffening influence of cholesterol in phospholipids is undoubtedly one of its major roles in biological membranes.
Tập 50 Số 9 - Trang 969-981 - 1972
STUDIES ON THE LIPID METABOLISM OF THE CHICK EMBRYO A study was made of the amounts and fatty acid compositions of the cholesterol esters, phospholipids, and triglycerides present in the yolk of the fertile unincubated egg and in the yolk, liver, and extrahepatic tissues of the chick embryo at various stages of development. Esterification of cholesterol, mainly with oleic acid, occurred in the yolk during incubation. There appeared to be a preferential absorption from the yolk sac of phospholipids rich in docosahexaenoic acid. Considerable amounts of cholesterol esters, of which 80% was cholesterol oleate, accumulated in the embryonic liver. The liver phospholipids contained more stearic, arachidonic, and docosahexaenoic acids, and less palmitic and oleic acids, than did the yolk phospholipids. Docosahexaenoic acid occurred in a surprisingly high concentration in the liver triglycerides. The extrahepatic triglycerides contained more palmitic and C18 polyunsaturated acids, but less docosahexaenoic acid, than did the liver triglycerides. The concentration of oleic acid in the extrahepatic cholesterol esters was much less than in the liver cholesterol esters. The extrahepatic phospholipids contained more arachidonic and docosahexaenoic acids, but less oleic acid, than did the yolk phospholipids. The implications of these findings are discussed in relation to the general lipid metabolism of the chick embryo.
Tập 42 Số 12 - Trang 1729-1741 - 1964
METABOLISM OF THE YOLK PHOSPHOLIPIDS BY THE DEVELOPING CHICK EMBRYO A study was made of the concentrations and fatty acid compositions of the various phospholipids in the yolks of fertile unincubated eggs and in the yolks of eggs that had been incubated for 13,15,17,19, and 21 days. Phosphatidyl choline and phosphatidyl ethanolamine accounted for 69 and 24% respectively of the total phospholipids present in the yolk of the unincubated egg. The remaining 7% was accounted for by small amounts of phosphatidyl serine, sphingomyelin, and a phospholipid fraction that was tentatively identified as diphosphatidyl glycerol. Although the percentage of total phospholipids in the total yolk lipid did not vary during incubation, there was a pronounced increase in the phosphatidyl choline: phosphatidyl ethanolamine ratio as incubation proceeded. The phosphatidyl ethanolamine fraction was the only phospholipid fraction present in the yolk that showed any consistent change in fatty acid composition during incubation. The concentration of docosahexaenoic acid in the fatty acids of the yolk phosphatidyl ethanolamine decreased from 8% on day 0 to 1.6% on day 21. It is suggested that the developing embryo preferentially absorbs from the yolk a phosphatidyl ethanolamine fraction that is relatively rich in docosahexaenoic acid.
Tập 43 Số 10 - Trang 1677-1686 - 1965
THE LIVER PHOSPHOLIPIDS OF THE DEVELOPING CHICK EMBRYO The concentrations and fatty acid compositions of the individual phospholipids in the livers of chick embryos on the 13th, 15th, 17th, 19th, and 21st days of incubation were compared with the concentrations and fatty acid compositions of the individual yolk phospholipids. The liver phospholipids contained higher proportions of phosphatidyl ethanolamine, phosphatidyl serine, and diphosphatidyl glycerol, and lower proportions of phosphatidyl choline, than did the yolk phospholipids. There was a constant increment (0.96 mg/day) of phosphatidyl choline in the liver during the period of incubation studied. The phosphatidyl choline, phosphatidyl ethanolamine, and phosphatidyl serine of the liver generally contained higher concentrations of stearic, arachidonic, and docosahexaenoic acids, and lower concentrations of palmitic and oleic acids than did these phospholipid fractions in the yolk. The fatty acid compositions of the sphingomyelin in the liver and yolk were similar. The most pronounced changes in the fatty acid composition of the liver phospholipids during embryonic development were observed in the phosphatidyl choline fraction. These changes suggested that the α-palmitoyl-β-arachidonyl phosphatidyl choline in the liver was gradually replaced by α-stearoyl-β-linoleoyl phosphatidyl choline and a-stearoyl-β-docosahexaenoyl phosphatidyl choline.
Tập 45 Số 5 - Trang 627-639 - 1967