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Biomedical subjects

N Asano

Publications and source records attributed to N Asano.

At least 127 records · Page 7Linked to original sources
PubMed1986

Chemical modification by diethylpyrocarbonate of an essential histidine residue in 3-ketovalidoxylamine A C-N lyase.

3-Ketovalidoxylamine A C-N lyase of Flavobacterium saccharophilum is a monomeric protein with a molecular weight of 36,000. Amino acid analysis revealed that the enzyme contains 5 histidine residues and no cysteine residue. The enzyme was inactivated by diethylpyrocarbonate (DEP) following pseudo-first order kinetics. Upon treatment of the inactivated enzyme with hydroxylamine, the enzyme activity was completely restored. The difference absorption spectrum of the modified versus native enzyme exhibited a prominent peak around 240 nm, but there was no absorbance change above 270 nm. The pH-dependence of inactivation suggested the involvement of an amino acid residue having a pKa of 6.8. These results indicate that the inactivation is due to the modification of histidine residues. Substrates of the lyase, p-nitrophenyl-3-ketovalidamine, p-nitrophenyl-alpha-D-3-ketoglucoside, and methyl-alpha-D-3-ketoglucoside, protected the enzyme against the inactivation, suggesting that the modification occurred at or near the active site. Although several histidine residues were modified by DEP, a plot of log (reciprocal of the half-time of inactivation) versus log (concentration of DEP) suggested that one histidine residue has an essential role in catalysis.

Amino Acids↗
PubMed1985

Purification and properties of 3-ketovalidoxylamine A C-N lyase from Flavobacterium saccharophilum.

3-Ketovalidoxylamine A C-N lyase was purified about 900-fold from the cell-free extract of Flavobacterium saccharophilum by ammonium sulfate fractionation, column chromatography on CM cellulose and gel filtration on Sephacryl S-200. The purified enzyme was homogeneous as judged by sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis. The molecular weight of the enzyme was estimated to be 36,000 by gel filtration on Sephacryl S-200 and by SDS polyacrylamide gel electrophoresis, indicating that the enzyme is a monomer. The optimum pH was found at 9.0. The enzyme activity was inhibited by EDTA or ethyleneglycol bis(beta-aminoethylether)-N,N'-tetraacetic acid and the inhibition was reversed by Ca2+ ion. The enzyme was able to eliminate p-nitroaniline or p-nitrophenol from p-nitrophenyl-3-ketovalidamine (IV) or p-nitrophenyl-alpha-D-3-ketoglucoside (VI), but not from p-nitrophenyl-1-epi-3-ketovalidamine or p-nitrophenyl-beta-D-3-ketoglucoside. Apparent Km values for IV and VI were 0.24 mM and 0.5 mM, respectively.

Bacterial Proteins↗
PubMed1984

Valiolamine, a new alpha-glucosidase inhibiting aminocyclitol produced by Streptomyces hygroscopicus.

Valiolamine, a new aminocyclitol has been isolated from the fermentation broth of Streptomyces hygroscopicus subsp. limoneus and its structure has been determined to be (1(OH),2,4,5/1,3)-5-amino-1-C-(hydroxymethyl)-1,2,3,4-cyclohexanetetr ol. Valiolamine has more potent alpha-glucosidase inhibitory activity against porcine intestinal sucrase, maltase and isomaltase than valienamine, validamine and hydroxyvalidamine which were reported as building blocks of validamycins and microbial oligosaccharide alpha-glucosidase inhibitors. In addition, valienamine, validamine and hydroxyvalidamine have been isolated from the fermentation broth.

Chemical Phenomena↗
PubMed1984

Microbial degradation of validamycin A by Flavobacterium saccharophilum. Enzymatic cleavage of C-N linkage in validoxylamine A.

The enzymatic cleavage of C-N linkage in the degradation of validamycin A by Flavobacterium saccharophilum was examined using N-p-nitrophenyl derivatives of validamine and valienamine as synthetic model substrates for validoxylamine A. Incubation of N-p-nitrophenylvalidamine with the membrane fraction from the organism led to formation of N-p-nitrophenyl-3-ketovalidamine, and succeeding cleavage of C-N linkage. As the products of the cleavage step, one was identified as p-nitroaniline and another keto compound could not be purified enough because of its instability. However, on the basis of its hydrogenation products, the structure of the keto compound could be established as 5D-(5/6)-5-C-(hydroxy-methyl)-2,6-dihydroxy-2-cyclohexen-1-one. The same experiment was carried out with N-p-nitrophenylvalienamine. In this case, N-p-nitrophenyl-3-ketovalienamine could be isolated as an intermediate but the desired keto compound from the cleavage step could not be isolated because of its instability. The participation of two enzymes, that is, a dehydrogenase and a C-N lyase on the cleavage of C-N linkage was assured, and moreover, the analysis of its products, together with those of the previous studies allow us to propose a degradation pathway of validamycin A by Flavobacterium saccharophilum.

Flavobacterium↗
PubMed1984

[Three cases of intracranial chordoma. Typical chordoma and chondroid chordoma].

Three cases of intracranial chordoma: 2 cases of typical chordoma and a case of chondroid chordoma, were reported and the clinico-pathological difference between these two types of chordoma was discussed. It is well known that typical chordoma is composed of physaliferous cells containing various quantities of intracytoplasmic mucin histologically, whereas chondroid chordoma as Heffelfinger reported in 1973 is composed of cellular area with scanty myxoid matrix and Chondroid matrix. Clinical course of the typical chordoma shows recurrence of the tumor within 2 years after surgical removal and radiation therapy in the majority of the cases, and the average survival range is said to be about 4.1 years, while chondroid chordoma takes benign course with average survival of 24.1 years after surgery and radiation therapy. One of our two patients with typical chordoma died from the recurrence two years after surgery and radiation therapy. However, the patients with chondroid chordoma showed no sign of recurrence over 2 years after subtotal removal and radiation. Surgical approach for the removal of the tumor was discussed as well. When the tumor is rather small and located at the upper clival region, transsphenoidal approach may be preferable, otherwise other approach should be chosen. When tumor has forward extension over the clivus, subtemporal approach will be most favorable with wider operative field. Identification of vessels and nerves around the tumor will be readily obtained by this approach.

Adult↗