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Biomedical subjects

M G Murray

Publications and source records attributed to M G Murray.

44 records · Page 3Linked to original sources
PubMed1978

Properties of pea seedling uracil phosphoribosyltransferase and its distribution in other plants.

A uracil phosphoribosyltransferase (UMP-pyrophosphorylase) was found in several angiosperms and was partially purified from epicotyls of pea (Pisum sativum L. cv. Alaska) seedlings. Its pH optimum was about 8.5; its required approximately 0.3 mm MgCl(2) for maximum activity but was inhibited by MnCl(2); its molecular weight determined by chromatography on Sephadex G-150 columns was approximately 100,000; its K(m) values for uracil and 5-phosphorylribose 1-pyrophosphate were 0.7 mum and 11 mum; and it was partially resolved from a similar phosphoribosyltransferase converting orotic acid to orotodine 5'-phosphate. Enzyme fractions containing both uracil phosphoribosyl transferase and orotate phosphoribosyltransferase converted 6-azauracil and 5-fluorouracil to products with chromatographic properties of 6-azauradine 5'-phosphate and 5-fluorouridine 5'-phosphate. Uracil phosphoribosyltransferase probably functions in salvage of uracil for synthesis of pyrimidine nucleotides.

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PubMed1978

Isolation and Characterization of a Chromatin-associated Protein Kinase from Soybean.

A chromatin-associated casein-type protein kinase has been purified 500-fold from soybean (Glycine max, var. Wayne) tissue. The enzyme can be completely dissociated from isolated chromatin in 250 millimolar (NH(4))(2)SO(4). After purification, the kinase preparation is stable for at least 6 months at 0 C. The enzyme will phosphorylate casein, phosvitin, and denatured chromatin proteins, but not histones. Only ATP will serve as a phosphate donor with an apparent K(m) of 8 micromolar. Five millimolar Mg(2+) is required for maximal activity, but Mn(2+) will support phosphorylation at a lower level. The average molecular weight as determined by sucrose gradient sedimentation and gel filtration is approximately 55,000. Under conditions of low ionic strength [less than 250 millimolar (NH(4))(2)SO(4)] soybean casein kinase forms higher molecular weight aggregates with other chromosomal proteins in the preparation. The enzyme activity is not affected by cyclic AMP. Casein kinase shows a broad optimum between 7 and 8 and the isoelectric point is approximately 9. Preliminary data indicate that soybean casein kinase will not phosphorylate soybean RNA polymerases I or II, nor does it have any obvious effect on in vitro chromatin transcription by endogenous RNA polymerases.

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PubMed1978

Isolation and preliminary characterization of a casein kinase from cauliflower nuclei.

A casein-type protein kinase has been isolated from cauliflower (Brassica cauliflora Gars.) nuclei and purified to a specific activity of 23,000 units/milligram of protein (1 unit is defined as the transfer of 1 picomole of (32)Pi from gamma-[(32)P]ATP to substrate per minute at 28 C). The enzyme has a molecular weight of approximately 39,000 as judged by sucrose density gradient sedimentation. The casein kinase requires ATP as the phosphate donor and will phosphorylate casein and phosvitin, but not histones. The enzyme activity is not affected by cAMP or cGMP. The casein kinase appears to be analogous to casein kinases described in other plant and animal systems.

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PubMed1971

Pyrimidine metabolism in cotyledons of germinating alaska peas.

Cotyledons from Pisum sativum L. cv. Alaska seeds were excised 12, 36, 108, 132, and 156 hours after imbibition in aerated distilled water. They were then incubated under aseptic conditions for 6 hours in solutions containing either uridine-2-(14)C or orotic acid-6-(14)C. Uridine was more extensively degraded to (14)CO(2) at all germination stages than was orotate, and these rates remained essentially constant at each stage. Incorporation of each compound into RNA increased about 2-fold from the 12th to the 156th hour, although the total RNA present decreased slightly over this interval. Paper chromatography of soluble labeled metabolites produced from orotate showed that the capacity to metabolize this pyrimidine increased markedly as germination progressed. Radioactivity in uridine-5'-P, uridine diphosphate-hexoses, and uridine diphosphate increased most, while smaller or less consistent increases in uridine, uracil, uridine triphosphate, and an unidentified UDPX compound were also observed. The data suggest that orotate metabolism was initially limited by orotidine-5'-phosphate pyrophosphorylase or by 5-phosphoribosyl-1-pyrophosphate. Incorporation of uridine into RNA appeared to be limited at the earliest germination periods by conversion of uridine-5'-P to uridine diphosphate. Thus, during the 1st week of germination the orotic acid pathway and a salvage pathway converting uridine into RNA become activated.

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PubMed1971

Development of Pyrimidine-metabolizing Enzymes in Cotyledons of Germinating Peas.

Mechanisms controlling conversion of orotic acid-6-(14)C to uridine-5'-phosphate in cotyledons of germinating Alaska peas (Pisum sativum L.) were investigated. The content of 5-phosphoribosyl-1-pyrophosphate was very low in dry seeds, increased to a maximum after about 12 hours of imbibition, and then rapidly declined. Orotidine-5'-phosphate pyrophosphorylase and orotidine-5'-phosphate decarboxylase activities more than doubled during the first 24 hours of germination and then also decreased. These results do not account for the continuous increases of orotate anabolism in such cotyledons as we observed previously. The initial increases in activities of these two enzymes were unaffected by cycloheximide, while the subsequent decreases were less rapid in the presence of this inhibitor. Activities of cotyledonary cytidine deaminase and uridine hydrolase also increased during imbibition, but the activity of only the latter showed a decrease after imbibition was completed. Cycloheximide inhibited the initial rapid increase in uridine hydrolase activity but had little effect on its subsequent decline. Cycloheximide had only slight inhibitory effects on the development of cytidine deaminase activity during the first 62 hours. The evidence suggests that uridine hydrolase might be synthesized de novo during the first few days of germination, but that the other three enzymes might not be.

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PubMed1965

Interconversions and production of volatile fatty acids in the sheep rumen.

1. Sheep fed at a constant rate were infused intraruminally with [1-(14)C]-acetate, -propionate or -butyrate during 5hr. periods. 2. Volatile fatty acids were estimated in the rumen contents and steady-state conditions were obtained. 3. Of the butyric acid carbon 60% was in equilibrium with 20% of the acetic acid carbon, and 2-3g.atoms of carbon were interconverted/day. 4. Little interconversion took place between propionic acid, acetic acid or butyric acid. 5. The net production rates for acetic acid, propionic acid and butyric acid were 3.7, 1.0 and 0.7moles/day respectively. 6. The production of volatile fatty acids accounted for 80% of the animal's energy expenditure.

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