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S Seto

Publications and source records attributed to S Seto.

At least 109 records · Page 6Linked to original sources
PubMed1979

Release of active and inactive renin by the human kidney.

1. Active and inactive renin were assayed in plasma of the renal veins and the inferior vena cava below the kidney in eight patients with hypertension and unilateral renal abnormalities, 20 min after the patients had resumed the upright position. 2. The concentration of active renin on the affected side was significantly higher than that on the non-affected side. The concentration of inactive renin on the affected side was significantly lower than that on the non-affected side and in the inferior vena cava. 3. These findings suggest either that the affected kidney mainly secretes active renin, which is then converted into inactive renin in the extrarenal circulation, or that the affected kidney activates inactive renin.

Enzyme Activation↗
PubMed1978

Purification and characterization of dimethylallyl pyrophosphate: aspulvinone dimethylallyltransferase from Aspergillus terreus.

Dimethylallyl pyrophosphate:aspulvinone dimethylallyltransferase, the prenylation enzyme for the biosynthesis of aspulvinone pigments, has been purified from mycelia of Aspergillus terreus. The transferase catalyzed the transfer of the dimethylallyl moiety from dimethylallyl pyrophosphate to either of the two aromatic rings of aspulvinone E to give the mono- and diprenylated derivatives which were identified with the metabolites aspulvinone I and aspulvinone H, respectively. Aspulvinone G, another fundamental metabolite of this series, also acted as substrate to afford the corresponding diprenylated derivative, which is assumed to be a precursor for aspulvinone C, D, and F. The molecular weight of the enzyme was estimated to be 240 000--270 000 by gel filtration. Since the subunit molecular weight determined by NaDodSO4-polyacrylamide disc gel electrophoresis was 45 000, the native enzyme appears to be a hexomeric protein composed of identical molecular weight subunits. The apparent Km values for aspulvinone E, aspulvinone G, and dimethylallyl pyrophosphate were 13.7, 7.7, and 40.0 micron, respectively. The enzyme shows the maximum activity at pH 7.0, and no metal ion is necessary for the activation. Sulfhydryl blocking agents or mercaptoethanol has no effect. Bromophenol blue binds specifically to the transferase and strongly inhibits the enzyme activity.

Alkyl and Aryl Transferases↗
PubMed1977

Solanesyl pyrophosphate synthetase from Micrococcus lysodeikticus.

Solanesyl pyrophosphate synthetase from extracts of Micrococcus lysodeikticus was purified by DEAE-Sephadex, hydroxylapatite, and Sephadex G-100 chromatography. This enzyme was found to catalyze the trans condensation of isopentenyl pyrophosphate with geranyl pyrophosphate to afford all-trans-octaprenyl (C40) and alltrans-nonaprenyl (C45) pyrophosphate without accumulation of prenyl pyrophosphate with chain length shorter than C40. all-trans-Farnesyl and all-trans-geranylgeranyl pyrophosphate also were active as cosubstrates, though they were less effective than geranyl pyrophosphate. However, neither dimethylallyl nor cis,trans,trans-geranylgeranyl pyrophosphate was active. The molecular weight of this enzyme was estimated to be 78 000 by Sephadex G-100 filtration. An enzyme preparation from young shoots of potato was found to hydrolyze the polyprenyl pyrophosphates effectively to give the corresponding prenols.

Alkyl and Aryl Transferases↗
PubMed1977

Two forms of farnesyl pyrophosphate synthetase from hog liver.

Two forms of farnesyl pyrophosphate synthetase were separated from hog liver extracts by DEAE-Sephadex chromatography. They were designated as farnesyl pyrophosphate synthetase A and B, in order of elution. Both enzymes catalyzed the exclusive formation of E,E-farnesyl pyrophosphate from isopentenyl pyrophosphate and either dimethylallyl pyrophosphate or geranyl pyrophosphate. They also showed no detectable differences in pH optima, molecular weights, and susceptibilities to metal ions. However, the catalytic activity of the synthetase B was greatly stimulated by the addition of common sulfhydryl reagents. This stimulation was the result of conversion of the synthetase B into the synthetase A. Conversely the synthetase A was converted into form B when it was dialyzed against a buffer solution containing cupric ions. It is suggested that the formation and cleavage of disulfide bond(s) is involved in the interconversion between the two forms.

Animals↗
PubMed1975

Comparative specificity of geranylgeranyl pyrophosphate synthetase of Micrococcus lysodeikticus and pumpkin.

Comparative studies on the substrate specificity of geranylgeranyl pyrophosphate synthetase from Micrococcus lysodeikticus and from pumpkin seedlin revealed that geranyl pyrophosphate was the most active of the natural substrates for the pumpkin enzyme, whereas it was the least active for the bacterial enzyme. A marked difference was also observed between the enzymes from these two sources as regards the reactivity of 3-methyl-2-alkenyl pyrophosphates as a function of the size of the alkyl group.

Kinetics↗