Biomedical subjects
Publications and source records attributed to K Murakami.
Insulin secretion induced by leucine and leucine plus glucose from rat pancreatic islets was enhanced by prior treatment with somatostatin antiserum as compared with normal rabbit serum in vitro. The results provide evidence that somatostatin plays an important role in insulin secretion in rats.
The kinetic and molecular properties of AMP deaminase [AMP aminohydrolase, EC 3.5.4.6] purified from baker's yeast (saccharomyces cerevisiae) were investigated. The enzyme was activated by ATP and dATP, but inhibited by Pi and GTP in an allosteric manner. Alkali metal ions and alkaline earth metal ions activated the enzyme to various extent. Kinetic negative cooperativity was observed in the binding of nucleoside triphosphates. Kinetic analysis showed that the number of interaction sites for AMP (substrate) and Pi (inhibitor) is two each per enzyme molecule. The molecular weight of the native enzyme was estimated to be 360,000 by sedimentation equilibrium studies. On polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate, the enzyme gave a single polypeptide band with a molecular weight of 83,000, suggesting that the native enzyme has a tetrameric structure. Baker's yeast AMP deaminase was concluded to consist of two "promoter" units which each consist of two polypeptide chains with identical molecular weight.
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We applied a "sandwich" method, with use of beads coated with anti-insulin serum and of peroxidase-labeled anti-insulin serum, to an enzyme immunoassay of insulin in human serum. 5-Aminosalicylic acid was used as the substrate for the enzymic reaction. As little as 5 milli-int. units of insulin per liter of serum insulin was detectable. Reproducibility was satisfactory, but extraordinarily high concentrations of proinsulin and of hydrogen donors such as reduced glutathione affect results of the assay. Values determined by our enzyme immunoassay and by double-antibody radioimmunoassay correlated highly (r = 0.938, p less than 0.001, n = 216). We recommend this method for use in the clinical laboratory.
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Alkaline reflux gastritis is presently accepted as being part of the postgastrectomy syndrome complex. Our experience with this entity has revealed a frequent association of alkaline reflux gastritis with functional or organic abnormalities of the gastric remnant and/or newly formed gastrojejunostomy. The role alkaline reflux gastritis plays as a separate entity in the symptomatic patient remains to be clinically determined.
The reoxygenation kinetics of the third generation C3H/He mouse mammary carcinoma has been studied and related to the time for 50% of irradiated tumors to regrow to the initial volume at irradiation (TRT-50) and to changes in tumor cell numbers. The experimental results suggest the following conclusions: (1) Fluctuations in TRT-50 values after two-dose irradiation under aerobic conditions are due to reoxygenation. (2) Since the TRT-50 after a second irradiation under hypoxic conditions remains independent of intervals between two doses for at least 3 days, repopulation and synchronization of surviving cells between irradiations is minimal. (3) A decreased cell number and/or cell loss from irradiated tumors is an important factor in tumor reoxygenation.
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In order to clarify the molecular basis of the unique features of rat renin (EC 3.4.99.19) and to provide materials and basic information for high blood pressure studies in rats, renin was purified from rat kidney. The final step of purification on CM-cellulose separated renin into three major isoenzyme peaks, R-I, R-II, R-III, and an additional minor peak. These preparations were judged homogeneous by multiple criteria, and the isoenzymes were found to have similar amino acid compositions. The amino acid composition is also closely analogous to hog renin, except that rat renin has a higher cysteine content. In contrast to hog renin, the rat enzymes do not contain amino sugars, yet are apparently glycoproteins as judged by their affinity for concanavalin A. The molecular weights of R-I, R-II, and R-III were estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis to be 37 000, 36 000 and 35 000, respectively. The isoelectric points were 5.05, 5.15 and 5.22, respectively. The specific activities of the purified enzymes (determined using rat plasma as substrate) were 615, 626 and 452 Goldblatt units/mg, respectively. Comparison of activities with the hog- and rat-derived substrates indicated a preference for that from the rat. The reaction of the rat enzymes with a synthetic peptide substrate had a similar catalytic rate constant to the hog enzyme, indicating close similarity in the active site region of the two enzymes.
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