Involvement of a cystatin-alpha-sensitive cysteine proteinase in the degradation of native L-lactate dehydrogenase and serum albumin by rat liver or kidney lysosomes.
A lysosomal cysteine proteinase plays a critical role in the lysosomal degradation of native L-lactate dehydrogenase. The effects of a recombinant cystatin alpha and other cysteine proteinase inhibitors on the degradation of unlabeled native L-lactate dehydrogenase by total lysosomal enzymes were examined in vitro. L-Lactate dehydrogenase was inactivated, its 35-kDa subunit disappeared and the final amino acid degradation products were produced during an incubation with disrupted lysosomes in vitro. These processes were all markedly suppressed by a small amount of cystatin alpha without inhibiting the activities of the known lysosomal cysteine proteinases, cathepsins B, H, L, and J. These results suggest that a cysteine proteinases, which is highly sensitive to cystatin alpha and distinct from other known lysosomal cysteine proteinases, is involved in the lysosomal degradation of native L-lactate dehydrogenase. An L-lactate-dehydrogenase-inactivating enzyme in the extracts of lysosomes was partially purified. It was separated from cathepsin J using a Sephacryl S-200 gel-filtration column and was further separated from cathepsin H by DEAE-Sephadex A-50 anion-exchange column chromatography. The inactivation and degradation of L-lactate dehydrogenase by this partially purified enzyme were all markedly suppressed by a low level of cystatin alpha without inhibiting the activities of both cathepsins B and L. The degradation of rat serum albumin by the partially purified enzyme was also inhibited by the same concentration of cystatin alpha. It is concluded that a cystatin-alpha-sensitive cysteine proteinase, other than cathepsins B, H, L and J, is present in lysosomes and functions in the lysosomal degradation of at least native L-lactate dehydrogenase and serum albumin.
Division of Enzyme Chemistry, University of Tokushima, Japan.
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Ohshita
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Kido
D000818:Animals; D015891:Cystatins / Q000494:pharmacology; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D005260:Female; D066298:In Vitro Techniques; D007668:Kidney / Q000378:metabolism; D007770:L-Lactate Dehydrogenase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D008099:Liver / Q000378:metabolism; D008247:Lysosomes / Q000378:metabolism; D008297:Male; D051381:Rats; D012709:Serum Albumin / Q000378:metabolism*
C070572:Csta protein, rat; D015891:Cystatins; D015853:Cysteine Proteinase Inhibitors; D012709:Serum Albumin; D007770:L-Lactate Dehydrogenase; D003546:Cysteine Endopeptidases