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Biomedical subjects

K Ishimaru

Publications and source records attributed to K Ishimaru.

At least 55 records · Page 3Linked to original sources
PubMed1988

Secretion in yeast of human lysozymes with different specific activities created by replacing valine-110 with proline by site-directed mutagenesis.

Computer graphics indicate that a steric hindrance exists between valine-110 side chain of human lysozyme (EC 3.2.1.17) and an acetyl group of a modified substrate that contains N6,O-diacetylmuramic acid. To alter the substrate specificity of human lysozyme to be effective on the modified substrate, we replaced the valine-110 residue with various amino acids by site-directed mutagenesis. One of the mutant proteins (valine residue replaced with proline:P110) was secreted in Saccharomyces cerevisiae as at least four components (P110-A, P110-B, P110-C, and P110-D) with different specific activities. Two components, P110-B and P110-D, were isolated in a pure form and structurally characterized. The results suggest that this mutation lowered the lytic activity against Micrococcus lysodeikticus by changing a local conformation of the catalytic site while keeping almost the same substrate binding sites. Our results also indicate that cis/trans isomerization of prolyl peptide bonds probably occurs in vivo and that the conformational change of protein as well as point mutations in genes might influence the molecular evolution of the protein.

Amino Acid Sequence↗
PubMed1985

Combined treatment with cisplatin and radiation therapy for mouse Cl 300 neuroblastoma.

The efficacy of the combined treatment of cisplatin and radiation therapy for mouse C1 300 neuroblastoma was studied. Intraperitoneal cisplatin injections and/or radiation were given from 7 to 21 days after inoculation of the tumor cells into the thigh region of A/Jax mice. The combination of 15 Gy radiation and 6 mg/kg cisplatin had an additive effect on both tumour growth delay and survival rate, while that of 30 Gy radiation and 6 mg/kg cisplatin had a synergistic effect. The efficacy of the combined therapy was dependent on the dose of radiation but not on the dose of cisplatin. The normal skin of the mouse was damaged in the similar pattern with both treatments. Thus, cisplatin has a potent radiosensitising effect in the treatment of mouse neuroblastoma.

Animals↗
PubMed1983

Cyclic adenosine 3', 5'-monophosphate, adenyl cyclase and phosphodiesterase in the conduction system of bovine heart.

Cyclic adenosine 3', 5'-monophosphate (cyclic AMP) and adenyl cyclase and phosphodiesterase activities were determined in the specialized myocardial tissue of the conduction system of bovine heart and then compared with those in the ordinary myocardial tissue. The conduction system was comprised of the atrioventricular node (A-V node), the His bundle and the right and the left bundle branches (RBB and LBB). The content of cyclic AMP was higher in the ordinary myocardial tissue than in the specialized myocardial tissue. In the specialized myocardial tissue, its content was highest in the A-V node and lower in the His bundle than in the LBB and the difference between the contents in the RBB and the LBB was not significant. Adenyl cyclase activity as well as the content of cyclic AMP was higher in the ordinary myocardial tissue than in the specialized myocardial tissue. Its activity was higher in the A-V node than in the His bundle or the RBB, and the activities in the His bundle, the RBB and the LBB were similar. Phosphodiesterase activity was higher in the ordinary myocardial tissue than in the A-V node, and the activities in these 4 sections of the conduction system were similar.

Adenylyl Cyclases↗
PubMed1983

Histidinomycin, a new antifungal antibiotic.

A new antifungal antibiotic named histidinomycin was isolated from the broth filtrate of a streptomycete, tentatively designated as isolate H 878-MY 1. Histidinomycin was purified as the monohydrochloride and the molecular formula was proposed to be C22H30N8O11.HCl. The antibiotic gave histidine by acid hydrolysis. Histidinomycin showed rather narrow antimicrobial spectrum for only few genera of phytophathogenic fungi.

Anti-Bacterial Agents↗
PubMed1983

New antibiotics, carbazomycins A and B. III. Taxonomy and biosynthesis.

The carbazomycin-producing microorganism, strain H 1051-MY 10, was determined to a strain of Streptoverticillium ehimense. Biosynthesis of carbazomycin B was studied using 14C-labeled and 13C-enriched precursors in combination with 13C NMR spectroscopy. The C-2 carbon of [2-13C]trytophan was shown to be involved at the C-3 carbon in carbazomycin B and both carbons of [1,2-13C]acetate at the C-1 and C-10 moiety of the antibiotic. [CH3-13C]Methionine was involved at the methoxyl group but not at the methyl group on the C-2 carbon of the antibiotic. Neither of the labeled carbons, [1-14C]tryptophan nor [2,3-13C]propionic acid, was detected in the antibiotic, and a progenitor of the C-2 and C-11 moiety of the antibiotic has not been determined.

Anti-Bacterial Agents↗
PubMed1983

Retrostatin, a new specific enzyme inhibitor against avian myeloblastosis virus reverse transcriptase.

A novel enzyme inhibitor against RNA-directed DNA polymerase of avian myeloblastosis virus was produced by an isolate of a new streptomycete for which the name Streptomyces retrostaticus is proposed. This enzyme inhibitor, which was named retrostatin, did not inhibit DNA-directed DNA polymerase of Escherichia coli and DNA-directed RNA polymerase of Ehrlich ascites tumor cells. Retrostatin was produced by the microorganism together with streptonigrin. These two substances were extracted from the culture broth with ethyl acetate at acidic pH. Retrostatin is an acidic pH indicator and the free acid was recovered as a red powder. Retrostatin had weak antibiotic activities against Gram-positive bacteria and yeasts.

Animals↗
PubMed1981

Mode of hydrolysis of diribonucleoside monophosphates by phosphodiesterase-phosphomonoesterase of Fusarium moniliforme.

The products derived from the degradation of the sixteen possible diribonucleoside monophosphates (NpN') by Fusarium phosphodiesterase-phosphomonoesterase were analyzed by means of thin layer chromatography. The analysis showed that NpN' was first cleaved into nucleoside N and 5'-nucleotide pN', which was then dephosphorylated to yield nucleoside N'. The dephosphorylation was fast when N' was adenosine or cytidine but slow when N' was guanosine or uridine. The cleavage reaction was followed by measuring the increase of absorbance due to hyperchromicity, and the kinetic constants, Km and kcat, were determined for the sixteen dinucleoside phosphates. The Km value was higher, for a given N, when N' was a pyrimidine nucleoside than when N' was a purine nucleoside. For a given N', uridine as N gave the highest Km value and adenosine gave the lowest one. The kcat value was the highest, for a given N, when N' was cytidine. For a given N', uridine as N gave by far the lowest kcat value. These results can be interpreted in terms of two binding sites on the enzyme with different base preferences. Comparison of kcat/Km values suggested that the base of nucleoside N plays an important role in determining whether a dinucleoside phosphate is a good substrate of the enzyme. The dinucleoside phosphates with uridine as N were found to be particularly poor substrates of the enzyme.

Chromatography, Thin Layer↗
PubMed1981

Cleavage of Trimeresurus flavoviridis phospholipase A2 with cyanogen bromide: sequence of the short peptide fragment and formation of a noncovalently bonded complex from the fragments.

Phospholipase A2 from the venom of Trimeresurus flavoviridis (Habu snake) on treatment with cyanogen bromide is split into less than Glu-Gly-Leu-Trp-Gln-Phe-Asn-Hse greater than, which is derived from the N-terminal moiety and is designated as S-peptide, and the remaining large peptide, which is designated as L-peptide. It should be stressed that the N-terminal residue is pyroglutamyl, unlike other phospholipases A2. The L-peptide alone was about 6% as active as the parent molecule. It occurs in dimeric form, like the parent molecule. When L-peptide was mixed with increasing amounts of S-peptide, the activity increased in a hyperbolic manner, indicating the formation of an ordered complex between L-peptide and S-peptide. The dissociation constant of the complex was 2.1 x 10(-7) M and its specific activity was 2.8 times that of L-peptide.

Amino Acid Sequence↗
PubMed1981

Molecular heterogeneity and biological activity of immunoreactive somatostatin in medullary carcinoma of the thyroid.

Two cases of somatostatin (SRIF)-producing medullary carcinoma of the thyroid are presented. The plasma levels of SRIF and calcitonin changed in accordance with the clinical course before and after resection of the tumor. On chromatographic analysis of tumor extracts derived from primary and metastatic tumors of medullary thyroid carcinoma, at least two components of immunoreactive SRIF (IR-SRIF) of large molecular size were found, besides a component corresponding to the tetradecapeptide (SRIF 14); one of these seemed to have almost the same molecular weight as the octacosapeptide (SRIF 28). Most of the IR-SRIF in one patient's plasma was eluted in the same position as tetradecapeptide SRIF. The biological activity of SRIF recovered from the tumor extract was assessed by measuring activity for inhibiting GH release using dispersed rat anterior pituitary cells. GH release from the cells into the incubation medium tended to decrease at a concentration of 1 x 10(-9) M IR-SRIF derived from the tumor (3000 +/- 482 ng/10(5) cells . 3 h) compared with the control value (4288 +/- 567 ng/10(5) cells . 3 h). A significant decrease was observed at concentrations of 1 x 10(-8) M (1880 +/- 403 ng/10(5) cells . 3 h) and 5 x 10(-8) M (938 +/- 262 ng/10(5) cells . 3 h). Responses to equivalent amounts of synthetic SRIF 14 were similar. This suggests that IR-SRIF in the tumor has almost the same biological activity as synthetic tetradecapeptide SRIF.

Adult↗
PubMed1980

Purification and properties of phospholipase A from venom of Trimeresurus flavoviridis (Habu snake).

Phospholipase A was purified from venom of Trimeresurus flavoviridis (Habu snake) via three steps consisting of Sephadez G-100, CM-cellulose, and DEAE-cellulose column chromatographies. The apparent molecular weights determined by gel filtration on Sephadex G-75 and by sodium dodecyl sulfate-polyacrylamide gel electrophoresis were 28,000 and 14,000, respectively, suggesting that the enzyme is composed of two identical subunits. The isoelectric point was 7.9. The enzyme is characterized by high contents of aspartic acid, glycine, tyrosine, and lysine and contains one residue each of histidine and methionine, three or four tryptophans, and eight disulfide bonds per subunit. The enzyme was inactivated by reaction with p-bromophenacyl bromide following pseudo first order kinetics. The loss of activity was accompanied by loss of histidine, indicating that a single histidine residue is essential for activity. Oxidation with N-bromosuccinimide decreased the enzymic activity. Tryptophan residues appear to play some role in catalysis.

Amino Acids↗
PubMed1980

Regulation of motilin secretion in the postprandial state in man.

The effect of various nutrients and hormones on motilin release was examined in normal volunteers and postvagotomy patients to investigate the mechanism of motilin secretion in the postprandial state. The ingestion of a mixed meal, protein and fat elevated the plasma motilin level, but the oral glucose load and arginine infusion lowered it. Although gastrin infusion showed no effect on the plasma motilin concentration, the infusion of insulin or glucagon inhibited motilin release in vivo. The patients, who underwent a selective or truncal vagotomy, also revealed a rise in plasma motilin after meal ingestion, suggesting that motilin could be released even in the absence of gastric acid and vagal stimulus. The perifusion experiments demonstrated that motilin release from human duodenal mucosa into the perfusate was stimulated markedly by low pH and 15 mM taurocholate, but not affected by the perifusion of 20 mM glucose, 20 mM arginine, 100 mU/l insulin or 30 nM glucagon. These results indicate that the motilin release induced by meal ingestion depend upon the balance of food components and that in normal subjects duodenal acidification, bile acid and unknown factors contained in the mixed meal may participate at least in part in postprandial motilin release. The inhibitory effect of glucose on motilin release may be attributable to a certain mediator mechanism which remains to be studied.

Adult↗
PubMed1980

New antibiotics, carbazomycins A and B. I. Fermentation, extraction, purification and physico-chemical and biological properties.

An unidentified Streptomyces, designated as Strain H 1051-MY 10, was proved to produce viomycin and two new antibiotics. The new antibiotics were extracted from the cultured mycelia with acetone and transferred to ethyl acetate after acetone was removed in vacuo. The extracted antibiotics were separated into two components by alumina column chromatography and named carbazomycins A and B, because both antibiotics were proved to contain a carbazole nucleus. The molecular formulae of carbazomycins A and B were determined to be C16H17NO2 and C15H15NO2, respectively. Further, carbazomycin B was methylated with diazomethane to give carbazomycin A. Carbazomycins inhibited the growth of phytophathogenic fungi and further showed weak antibacterial and antiyeast activities.

Animals↗