Post-proline endopeptidase. Interaction of the enzyme with substrates containing disulfide and thioether bond

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Abstract
The free thiol group of post-proline endopeptidase (EC 3.4.21.26) can interact with the disulfide bridge contained in some of the substrates of this enzyme (neurohypophysial hormones and some of their analogues). The influence of these interactions on the activity of this enzyme was studied using several substances modelling individual types of interactions: thiol-disulfide exchange, catalytic interaction and a complex interaction including the two preceding types. Deamino-1-carba-oxytocin is catalytically hydrolysed in the concentration range up to 10-3mol/l, oxytocin and arginine-vasopressin are catalytically hydrolysed in concentrations of 10-5 to 10-8 mol/l. A reaction leading to inactivation of the enzyme prevails at concentrations of 10-3 to 10-4 mol/l. When inactivated by lower concentrations of arginine-vasopressin (up to a molar ratio of 1 : 1), the enzyme can be reactivated by incubation with dithiothreitol, higher concentrations of arginine-vasopresson cause irreversible enzyme inactivation.

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