Actomyosin prepared from the ordinary muscle of pacific mackerel
Scomber japonicus was denatured by the crude enzymes obtained from the above mentioned muscle of mackerel at pH 5.0 in the presence and the absence of pepstatin, the typical inhibitor of cathepsin D. Thus, it has been presumed that other than cathepsin D there were some proteases which denatured the actomyosin of the ordinary muscle of pacific mackerel at about pH 5.
Optimum pH's of hemoglobin substrate were 5.4 being measured by the Cu-Folin method and at 5-6 by the ninhydrin one.
The enzymes fractionated by Sephadex G-75 column chromatography, were inhibited by leupeptin and iodoacetic acid and slightly activated by L-cysteine. From this result, it has been assumed that the enzymes would be acid thiol proteases.
The enzymes hydrolyzed the synthetic substrate Z-Phe-Arg-MCA which is sensitive to both cathepsins B and L, but inactive on Arg-MCA which is known to be susceptible to cathepsin H.
From these results, it has been confirmed that there were acid thiol proteases which denatured or autolyzed the actomyosin of the ordinary muscle of pacific mackerel, and that the proteases might be cathepsins B or L, or the like.
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