NoteNative in theand Acid - denatured L - Lactate Dehydrogenase Are Different Lysosomal Proteinases Involving in Their Overall Degradatjon JSasA

VVhen native and acid-denatured Jactate dehydregenase (LDH) were incubated with total lysosomal enzymes in vitro, amino acids from their degradation were produced at various acidic pH. The pH profile in the overall degradation of natiye LDH was markedly different from that of acid-denatured LDH. Disappearance of the 35-kDa subunit of native LDH was markedly suppressed by a low level of cystatin a as well as by a general cysteine proteinase inhibitor, N-(L3-trans-carboxyoxirane-2-carbollyl)-L-lellcine-3-methylbutylamide (E-64-c). On the other hand, the degradation of acid-denatured LDH was only slightly suppressed by tltese inhibiters. It was concluded that at least a part of the proteinases inyolyed in the overall degradation of natiye LDH is different from the proteinases involved in the degradation of acid-denatured form and a role of a cystatin a-sensitive cysteine proteinase is critical in the lysosomaJ degradation of natiye LDH, but not in that of acid-denatured form.