PubMed Health⌕ Search

Biomedical subjects

T Hama

Publications and source records attributed to T Hama.

At least 91 records · Page 5Linked to original sources
PubMed1980

Rapid chromatographic purification of dipeptidyl peptidase IV in human submaxillary gland.

Pure dipeptidyl peptidase IV (X-prolyl dipeptidyl aminopeptidase), which did not contain aminopeptidase activity at all, was rapidly prepared from the human submaxillary gland by chromatography with concanavalin A-Sepharose and Gly-Pro-NH-(CH2)6-NH-Sepharose. The entire purification took only 3 days. Aminopeptidase, which was very difficult to separate from dipeptidyl peptidase IV by various chromatographic procedures, could be completely removed by chromatography with Gly-Pro-NH-(CH2)6-NH-Sepharose. On SDS gel electrophoresis the purified enzyme gave a single band with a molecular weight of 116,000. The apparent molecular weight of the enzyme was estimated to be 225,000 by gel filtration. Therefore, the enzyme consists of two identical subunits. It did not hydrolyze Ala p-nitroanilide at all, but the hydrolysis of the p-nitroanilides of Gyl-Pro, Lys-Pro and Arg-Pro at pH 8.0 was nearly specific.

Chromatography, Gel↗
PubMed1980

Induction of precocious melanogenesis of pigment cells in cultures of neuroretinal cells of chick embryo by amphotericin B.

When dissociated neuroretinal cells of the 9-day-old chick embryo were cultured, the cells formed monolayer sheets of somewhat flattened epithelial cells within 15 days after inoculation. During 15 to 30 days, numerous foci of non-pigmented epithelial cells were formed. During 30 to 50 days, melanin appeared in the cells of these foci. When amphotericin B (1 microgram/ml) was added to the culture medium on day 25 of culture, brown pigments appeared precociously, i.e. within the first two days, in the cells. The brown pigments were identified as melanins by histochemical and electron-microscopic methods. Induction of melanogenesis required continuous treatment with amphotericin B. With the precocious appearance of melanins, tyrosinase activity increased rapidly. This rapid increase in tyrosinase activity was inhibited by the addition of phenylthiourea or diethyl-dithiocarbamate. It was not enhanced by iodoacetamide, but was blocked by a low concentration of cycloheximide or actinomycin D. These findings indicate that amphotericin B induces de novo synthesis of tyrosinase rather than activation of pre-existing tyrosinase.

Amphotericin B↗
PubMed1980

Activation of rabbit muscle fructose 1,6-bisphosphatase by histidine and carnosine.

Histidine and its derivatives increased rabbit muscle fructose 1,6-bisphosphatase activity at neutral pH with positive cooperativity. In the presence of histidine and carnosine the optimum pH shifted from pH 8.0 to 7.4. The cooperative response of the enzyme to AMP and fructose 1,6-bisphosphate was observed in the presence of the histidine derivatives. Of a number of divalent cations tested, only Zn2+ was found to be an effective inhibitor of enzyme activity at low concentrations. The kinetic data suggested that Zn2+ acted as inhibitor as well as activator for the enzyme activity; a high affinity binding site was associated with Ki of approximately 0.5 microM Zn2+ and a catalytic site was associated with Km of approximately 10 microM Zn2+. Rabbit muscle fructose 1,6-bisphosphatase bound 4 equivalents of Zn2+/mol, presumably 1 per subunit, in the absence of fructose 1,6-bisphosphate. Two equivalents of Zn2+/mol bound to the enzyme were readily removed by dialysis or gel filtration in the absence of a chelating agent. The other two equivalents of Zn2+/mol were removed by histidine and histidine derivatives of naturally occurring chelators with concomitant increase in activity.

Animals↗
PubMed1980

Mild purification procedure and subunit structure of glucosephosphate isomerase from baker's yeast.

A mild procedure for the purification of glucosephosphate isomerase from baker's yeast (Saccharomyces cerevisiae) is reported. The purified enzyme was homogeneous and did not contain charge isomers as shown by polyacrylamide gel electrophoresis as well as DEAE-Sepharose column chromatography. Its molecular weight determined by gel filtration and sucrose density gradient centrifugation was approximately 120 000, which agreed with that of the enzyme in the crude extract as well as that of the renatured enzyme. Gel filtration in 6M guanidine/HCl as well as acrylamide gel electrophoresis of sodium dodecyl sulfate denatured glucosephosphate isomerase showed one single peak and gave a subunit molecular weight of 60 000. Cross-linking patterns obtained with yeast glucosephosphate isomerase after treatment with dimethyl suberimidate resulted in the appearance of dimers as the largest-linked product of the enzyme subunit. After dissociation the enzyme can readily be reassociated and renatured with a yield of maximum 73% and a pseudo first order rate constant of 0.12 min-1 at 25 degrees C.

Chemical Phenomena↗