Search PubMed⌕ Search

Biomedical subjects

K Akashi

Publications and source records attributed to K Akashi.

At least 163 records · Page 9Linked to original sources
PubMed1984

pH dependence of salt activation of human leukocyte elastase.

The effects of pH on salt stimulation of the rates of hydrolysis of three substrates by human leukocyte elastase were studied. The enzyme was most active at pH 10.5, 8.0-8.5, and 9.5 for the hydrolyses of fluorescein isothiocyanate-labeled S-carboxymethylated bovine serum albumin (FITC-CM-BSA), succinyl-L-Ala-L-Pro-L-Ala-7-methylcoumaryl-4-amide (Suc-APA-MCA), and succinyl-L-Ala3-p-nitroanilide (Suc-Ala3-pNA), respectively, in the absence of NaCl. The enzyme was activated by 0.5 M NaCl similarly at all pHs tested for the hydrolysis of Suc-Ala3-pNA, but more at neutral and alkaline pH values, respectively, for the hydrolyses of FITC-CM-BSA and Suc-APA-MCA. Thus, in the presence of 0.5 M NaCl, the enzyme was most active at pH 8.0 and 10.0 with FITC-CM-BSA and Suc-APA-MCA, respectively. In contrast, the proteolytic activity of porcine pancreatic elastase was somewhat inhibited by 0.5 M NaCl.

Enzyme Activation↗
PubMed1983

Production of human interferon-gamma in serum-free medium.

Interferon (IFN)-gamma was produced with a high yield in cultures of human peripheral mononuclear cells by combined stimulation with OK-432 and staphylococcal enterotoxin B. Human mononuclear cells cultured in serum-free medium produced several times as much IFN as those in RPMI-1640 medium containing 10% fetal bovine serum. A synergistic effect of OK-432 and staphylococcal enterotoxin B on the production of IFN-gamma was demonstrated. Ultrogel AcA54 column chromatography of crude IFN showed a single peak with an apparent molecular weight of 43,000. Our production system for human IFN-gamma offers a feasible approach to preparation of large quantities of purified IFN-gamma for structure studies, antibody production, and clinical applications.

Blood↗
PubMed1978

Determination of redox potential levels critical for cell respiration and suitable for L-leucine production.

The effect of oxygen supply on L-leucine fermentation was investigated employing a leucine-producing mutant of Brevibacterium lactofermentum. Since it was not possible to measure oxygen tension below 0.01 atm by a Teflon-coated oxygen electrode, the degree of satisfaction of the cells' oxygen demand (cells' respiration rate/maximum oxygen demand of cells, rab/KrM) and the redox potential of the culture medium (E, mV) were used as indices to oxygen supply in cultures under low oxygen tension. When the oxygen demand of the cells was satisfied (rab/KrM = 1.0) and the E value was between --90 and --110mV, L-leucine formation was 26.5 mg/ml. When the oxygen demand of the cells was not satisfied (rab/KrM = 0.85) and the E value was between --200 and --220 mV, L-leucine accumulation was 29.7 mg/ml. When the oxygen supply was extremely limited (rab/KrM = 0.27) and the E value was --280 mV, L-leucine formation was 12.9 mg/ml. A new method which simultaneously measures the redox potential and dissolved oxygen was applied to the determination of the critical dissolved oxygen level for cell respiration (PL crit), whick was too small to be detected by conventional oxygen electrodes. The value of PL crit of the leucine producer was estimated as 0.0002 atm.

Brevibacterium↗
PubMed1978

Enzyme-bound formylvaline and formylvalylglycine; an initiation complex for gramicidin A biosynthesis.

Gramicidin A is an antibiotic peptide produced by Bacillus brevis ATCC 8185, which also produces tyrocidines. An attempt was made to establish a cell-free enzyme system for gramicidin A synthesis. An enzyme fraction, Component I, was partially purified from crude extracts of the organism and proven to be involved in the synthesis of the formyl-Val-Gly- region of gramicidin A. The initiation of gramicidin A biosynthesis is a function of Component I, which activates valine and binds it as a thioester, and further formylates it in the presence of formyltetrahydrofolic acid. The formylvaline thus synthesized is transferred to the glycine moiety, which is also thioesterified to Component I. Elongation of the peptide chain takes place by a mechanism similar to those found for tyrocidines, gramicidin S, and bacitracin.

Aminoacylation↗
PubMed1977

Biosynthesis of enzyme-bound formylvaline and formylvalylglycine. A possible initiation complex for gramicidin A biosynthesis.

A partially purified fraction (Component I) which catalyzed the ATP-PPi exchange reaction dependent only on valine and glycine among the five constituent amino acids of gramicidin A was obtained from crude extracts of Bacillus brevis ATCC 8185, which produces both gramicidin A and tyrocidines. This fraction was found to bind valine and glycine as thioesters. The addition of a formylTHFA synthesizing system to Component I brought about the formation of Component I-bound formylvaline and formylvalylglycine.

Bacillus↗