[Insulin-degrading neutral proteinases of the plasma membrane of loach liver and embryo cells].

Insulin-degrading, Ca2+-activated, neutral proteinases of molecular weight about 150 kDa and 70 kDa were purified from plasma membranes of the loach liver and embryo cells. It was shown that dithiothreitol and cysteine enhanced the enzyme activity, whereas p-chloromercuribenzoate and iodoacetic acid inhibited its level. Incubation of isolated plasma membranes with 5'[gamma 32P]ATP resulted in phosphorylation of these proteinases. The intensity of the process increased under the influence of insulin (100 microU/ml), that correlated with a decrease in the activity of proteinase with molecular weight of 150 kDa and an increase in 70 kDa enzyme activity. The data suggest the existence of common regulatory pathways of insulin degradation in plasma membranes of the loach liver and embryo cells.