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Biomedical subjects

T Kozu

Publications and source records attributed to T Kozu.

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

Heterogeneous forms of poly(rA) . oligo(dT)-directed DNA polymerase activity from rat spleen.

Three forms of DNA polymerase, named enzymes A, B, and C, that preferred (rA)n x (dT)12-18 as a template-primer, were partially purified from an extract of rat spleen. Enzymes B and C, both sedimenting at 9S, appeared to correspond to DNA polymerase gamma. However, they differed in their behavior on phosphocellulose and DNA-cellulose column chromatographies, and in their optimum KCl and divalent cation requirements for activity. Enzyme A showed a unique property. Like DNA polymerase beta, it sedimented at 3.8S, was resistant to reagents blocking sulfhydryl groups, and was inhibited by phosphate, but it differed from DNA polymerase beta with respect to elution positions from DEAE-cellulose, phosphocellulose and DNA-cellulose columns, Km value (lower by one order of magnitude for dTTP), and template-primer preference. Enzyme A was found in the mitochondrial fraction, in which DNA polymerase beta was not detectable. Enzymes A and C were isolated from the nuclear fraction, but this fraction did not contain enzyme B. The cytosol contained only enzyme A. The mitochondrial fraction contained enzyme A and enzyme C-like polymerase. Enzyme B was obtained with enzymes A and C only by extraction of the whole cell homogenate. Enzyme B may be labile or may be an artificial form of DNA polymerase gamma formed during the purification procedures.

Animals↗
PubMed1981

Inhibition of DNA polymerases alpha and gamma by rifamycin derivative AF/013.

The nature of the inhibitory effects of rifamycin derivative AF/013 (O-n-octyloxime of rifamycin SV) on DNA polymerases alpha and gamma were studied. Lineweaver-Burk analysis of the inhibition of DNA polymerases with respect to a substrate and template-primer showed a different mode of inhibition by AF/013 for each: the inhibition of DNA polymerase gamma was competitive with both dTTP and poly(rA)-oligo(dT), while that of DNA polymerase alpha was competitive with activated calf thymus DNA and non-competitive with dTTP. Further analysis of the competitive mode of the inhibition of DNA polymerase alpha, using poly(dT)-oligo(rA) as a template-primer, demonstrated that the primer molecule competed with AF/013. A change of effective divalent metal ion (Mn2+ in place of Mg2+) in the reaction mixture did not alter this competitive mode of inhibition with respect to the template-primer. The results of experiments to obtain further insight into the mechanism of drug-enzyme interaction suggest that AF/013 binds tightly to DNA polymerase alpha, and inhibits the process of chain elongation with DNA polymerases alpha and gamma.

Animals↗
PubMed1978

Substrate specificity for pancreatic amylase.

Substrates commonly used for the determination of amylase activity include potato starch, corn starch and dye-labeled starch. Determination of the amylase activity of serum using these different starches has shown that the measured value varies depending upon the ratio of isoamylases present, namely between pancreatic amylase (P-type) and salivary amylase (S-type), contained in the serum. With corn starch as substrate, the P-type dominant serum exhibited an apparently higher value than the S-type dominant serum. In the use of blue-starch which is employed as a chromogenic method, the P-type dominant serum gave a higher value than the S-type dominant serum. Red-starch which is also used as a chromogenic method, however, did not cause the P-type dominant serum to show such a high level of amylase activity as blue-starch. These differences in amylase activity can be also shown by determining the Km values of pancreatic amylase and salivary amylase using these substrates. Thus, corn starch and blue-starch showed smaller Km values to pancreatic amylase than to salivary amylase. They were thus proved to have a strong affinity for pancreatic amylase. In contrast, potato starch, red-starch and glycogen had good affinity for salivary amylase. In pancreatic disease in which pancreatic amylase is increased without much elevation in the total amylase level in the serum, it might be possible to detect the abnormality of pancreatic amylase activity if either corn starch or blue-starch is used as a substrate for measurement of the serum amylase activity.

Amylases↗