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Biomedical subjects

S Doonan

Publications and source records attributed to S Doonan.

At least 73 records · Page 4Linked to original sources
PubMed1981

Cleavage by trypsin and by the proteinase from Armillaria mellea at epsilon-N-formyl-lysine residues.

Kinetic studies were made of the hydrolysis by trypsin of alpha-N-acetylglycyl-L-lysine methyl ester and of its neutral analogue alpha-N-acetylglycyl-epsilon-N-formyl-L-lysine methyl ester. The latter substance is a moderately good substrate for trypsin, and this observation is discussed in terms of the substrate specifically of the enzyme. The actions of trypsin and of the lysine-specific proteinase from Armillaria mellea on both a native and a formylated polypeptide substrate were compared. Both enzymes were found to hydrolyse specifically bonds to epsilon-N-formyl-lysine in the formylated substrate.

Agaricales↗
PubMed1980

Selective permeability of rat liver mitochondria to purified malate dehydrogenase isoenzymes in vitro.

1. The mitochondrial malate dehydrogenase from rat liver has been purified to a state of homogeneity as judged by starch-gel electrophoresis and the cytoplasmic isoenzyme has been obtained in a partically purified state. 2. Inhibition of the isoenzymes by sulphite has been studied. 3. In mitochondria loaded with sulphite, the catalytic activity of the (partially inhibited) internal malate dehydrogenase has been measured by addition of oxaloacetate to the suspension medium and observation of the consequent decrease in fluorescence of NADH. 4. Addition of mitochondrial malate dehydrogenase to suspensions of mitochondria loaded with sulphite resulted in an increase in the level of intramitochondrial enzymic activity as measured by the above technique. Addition of the cytoplasmic isoenzyme did not result in such an increase. 5. These results show that mitochondria in suspension are permeable to the mitochondrial malate dehydrogenase but not to the cytoplasmic isoenzyme. 6. This conclusion has been confirmed by direct measurement of a decrease of enzyme activity in solution and an increase inside the mitochondria after incubation of organelles in solutions containing mitochondrial malate dehydrogenase. No such effect was observed with the cytoplasmic isoenzyme. 7. Some features of the permeation process have been studied.

Animals↗
PubMed1979

Urinary inhibitor of the formation of calcium oxalate.

Normal urine was examined for substances which inhibited the formation of calcium oxalate, using a separation scheme which involved ultrafiltration, alcohol precipitation, electrophoresis and paper chromatography. The major anionic inhibitors were found to be citric acid, isocitric acid and pyrophosphate. The inhibitory activity of urine and that of an artificial urine having the same concentration of urea, creatinine, sodium, potassiu, magnesium, calcium, ammonia, sulphate, chloride, inorganic phosphate, oxalate, citrate, isocitrate and pyrophosphate, and the same pH were identical. This confirmed that urine does not contain an unidentified potent substance which inhibits the formation of calcium oxalate.

Calcium Oxalate↗
PubMed1978

Isolation and identification of some urinary inhibitors of calcium phosphate formation.

Normal urine has been examined for substances which inhibit formation of calcium phosphate. A separation scheme involving ultrafiltration, precipitation, electrophoresis and paper chromatography was devised to isolate these substances. Contrary to what has been suggested in the literature for many years, the urines examined did not contain a potent unidentified inhibitor. The major anionic inhibitors were citric acid, pyrophosphate and isocitric acid. These substances together with a small contribution from the cations appeared to account for most, if not all, of the inhibitory activity of urine.

Adult↗
PubMed1977

Selective permeability of rat liver mitochondria to purified aspartate aminotransferases in vitro.

1. A method was devised to allow determination of intramitochondrial aspartate amino-transferase activity in suspensions of intact mitochondria. 2. Addition of purified rat liver mitochondrial aspartate aminotransferase to suspensions of rat liver mitochondria caused an apparent increase in the intramitochondrial enzyme activity. No increase was observed when the mitochondria were preincubated with the purified cytoplasmic isoenzyme. 3. These results suggest that mitochondrial aspartate aminotransferase, but not the cytoplasmic isoenzyme, is able to pass from solution into the matrix of intact rat liver mitochondria in vitro. 4. This system may provide a model for studies of the little-understood processes by which cytoplasmically synthesized components are incorporated into mitochondria in vivo.

Ammonium Chloride↗
PubMed1976

An assessment of some of the methods available for the determination of molecular weights of proteins as applied to aspartate aminotransferase from pig heart.

The isopotential specific volume of cytoplasmic aspartate aminotransferase from pig heart was found to be 0.763 ml g-1 whereas the value of the apparent specific volume obtained by summation of contributions from each type of amino acid in the protein is 0.735 ml g-1. Use of the experimentally determined isopotential specific volume largely abolishes the discrepancy between a previously reported value of the molecular weight of the native (dimeric) enzyme and that of the enzyme subunit obtained from its primary structure (46300). A new non-empirical method based on quantitative N-terminal analysis involving radioisotope dilution is described for the determination of subunit molecular weight of proteins. The method is capable of considerable accuracy and sensitivity. Some of the methods available for the determination of molecular weights ans subunit compositions of proteins are discussed.

Amino Acid Sequence↗