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Biomedical subjects

S M Byun

Publications and source records attributed to S M Byun.

46 records · Page 3Linked to original sources
PubMed1990

Purification and properties of ampicillin acylase from Pseudomonas melanogenum.

Ampicillin acylase, which is known to have a novel substrate spectrum, was purified to homogeneity from Pseudomonas melanogenum by the crude extract preparation and chromatography with S-Sepharose, hydroxyapatite, CM-cellulose C-52, and CM-Sepharose. The molecular weight of the native enzyme was calculated to be 146,000 by Protein PAK-300 sw HPLC chromatography. SDS-polyacrylamide gel electrophoresis revealed that the enzyme consisted of two identical subunits with a molecular weight of 72,000. The enzyme was a glycoprotein containing 13% of total carbohydrate, and its isoelectric point was 7.2. The enzyme catalyzed both synthesis and hydrolysis of ampicillin and hydrolysis of the ester bond of phenylglycinemethylester hydrochloride substrate. The substrate specificity showed that the enzyme required a free amino group on the alpha-carbon of the acyl group. Chemical modification by diethylpyrocarbonate or N-bromosuccinimide resulted in time-dependent inactivation of the enzyme, and other results suggest the participation of essential histidine residue(s) in the catalytic activity of ampicillin acylase. Substrates of the enzyme, 6-aminopenicillanic acid and ampicillin, exhibited protective effects against N-bromosuccinimide inactivation, suggesting that the modification occurred near or at the active site.

Amidohydrolases↗
PubMed1990

Evidence for involvement of 2 histidine residues in the reaction of ampicillin acylase.

The chemical modification of purified ampicillin acylase by N-bromosuccinimide and diethylpyrocarbonate resulted in time-dependent inactivation of the enzyme. Both substrates, ampicillin and 6-aminopenicillanic acid, protected the enzyme against inactivation, suggesting that the modification occurred near or at the active site. Amino acid analyses and other data indicated that two histidyl residues per subunit molecule were essential for catalytic activity.

Amidohydrolases↗
PubMed1989

Site-specific alteration of Gly-24 in streptokinase: its effect on plasminogen activation.

Oligonucleotide-directed mutagenesis was carried out to replace glycine-24 of streptokinase with histidine, glutamic acid, or alanine. Substitutions with either histidine or glutamic acid resulted in almost complete loss of streptokinase activity but streptokinase replaced with alanine retained its activity. Although streptokinases with histidine-24 or glutamic acid-24 bound normally to human plasminogen, they were not able to generate active plasmin, whereas those with alanine-24 or glycine-24 (wild-type) could generate active plasmin. The results indicate that the small, uncharged alkyl group side-chain on the 24th amino acid residue of streptokinase is indispensable for the activity of the human plasminogen-streptokinase complex.

Alanine↗
PubMed1987

Nucleotide sequences of immunoglobulin epsilon genes of chimpanzee and orangutan: DNA molecular clock and hominoid evolution.

To determine the phylogenetic relationships among hominoids and the dates of their divergence, the complete nucleotide sequences of the constant region of the immunoglobulin epsilon-chain (C epsilon 1) genes from chimpanzee and orangutan have been determined. These sequences were compared with the human epsilon-chain constant-region sequence. A molecular clock (silent molecular clock), measured by the degree of sequence divergence at the synonymous (silent) positions of protein-encoding regions, was introduced for the present study. From the comparison of nucleotide sequences of alpha1-antitrypsin and beta- and delta-globin genes between humans and Old World monkeys, the silent molecular clock was calibrated: the mean evolutionary rate of silent substitution was determined to be 1.56 X 10(-9) substitutions per site per year. Using the silent molecular clock, the mean divergence dates of chimpanzee and orangutan from the human lineage were estimated as 6.4 +/- 2.6 million years and 17.3 +/- 4.5 million years, respectively. It was also shown that the evolutionary rate of primate genes is considerably slower than those of other mammalian genes.

Animals↗
PubMed1983

Immobilization of urokinase on agarose matrices.

Immobilization of urokinase, a plasminogen activator, was carried out to determine the effect of spacer length used on the immobilized enzyme activity. The enzyme was covalently coupled to agarose gel, both directly to the matrix and also via interposing different lengths of spacer groups. The specific activity of immobilized urokinase increased as the spacer length (n') increased to a certain length and tended to decrease thereafter. The maximal activity was shown when the value of n' was 7 for the agarose-NH-(CH2)n-CO-NH-(CH2)2-CO-NH-urokinase series. The coupling yield of the enzyme activity was from 33 to 68% depending on various forms of immobilized urokinase. The immobilized urokinase was characterized with regard to pH, temperature, storage, and thermal stabilities.

Endopeptidases↗
PubMed1982

Estimation of free myo-inositol in milks of various species and its source in milk of rats (Rattus norvegicus).

Free myo-inositol content of milk of rats and other rodents fed standard laboratory chow is 80 mg/100 g as compared to about 4 mg/100 g for cow milk. Feeding experiments with graded amounts of myo-inositol demonstrated that the myo-inositol content of milk is strongly influenced by dietary intake. Radioactivity from either [carbon-14] glucose or [hydrogen-3] myo-inositol injected intraperitoneally was incorporated rapidly into milk myo-inositol. Thus, both mammary biosynthesis and active transport contribute to the high myo-inositol in rat milk, but the latter is quantitatively the more important.

Animals↗
PubMed1981

Stereospecificity of L-myo-inositol-1-phosphate synthase for nicotinamide adenine dinucleotide.

Partially purified preparations of L-myo-inositol.-1-phosphate synthase (EC 5.5.1.4) from testis and mammary gland of laboratory rats (Rattus norvegicus) were used to show that this enzyme is specific for the pro-S hydrogen at C-4 of its cofactor, nicotinamide adenine dinucleotide (NAD). pro-S specificity of the first step (reversible oxidation of glucose 6-phosphate to 5-ketoglucose 6-phosphate) was proved by showing that tritium is transferred from [pro-S-4-3H]NADH but not from [pro-R-4-3H]NADH to glucose 6-phosphate when they are incubated with enzyme. That the stereospecificity in the second oxidation--reduction step (reduction of myo-inosose-2 1-phosphate to myo-inositol 1-phosphate) is the same as in the first step was shown by demonstrating that tritium from [5-3H]glucose 6-phosphate is incorporated into myo-inositol but not into NAD+ and that tritium from [4-3H]NAD+ is not incorporated into myo-inositol

Animals↗