Characteristics of an acetone powder preparation of the vitamin K-dependent γ-glutamyl carboxylase

Abstract

An acetone powder, prepared from the liver microsomes of vitamin K-deficient rats, retains an active vitamin K-dependent γ-glutamyl carboxylase. While the basic requirements of the enzyme are similar to those of the carboxylase of either resuspended microsomes or detergent-solubilized microsomes, the acetone powder preparation reveals some additional properties of the carboxylase. Carboxylation of the synthetic pentapeptide substrate phenylalanyl-leucyl-glutamyl-glutamyl-valine can occur in the absence of nonionic detergent; however, when vitamin K hydroquinone drives the acetone powder carboxylation nonionic detergent is required for maximal activity. Experiments are described in which the acetone powder is incubated with the pentapeptide, pelleted by centrifugation, resuspended with fresh reactants, and incubated again. They suggest that the low V for the carboxylase, observed by all investigators, is, at least in part, not the result of irreversible enzyme inactivation nor depletion of reactants, but rather accumulation of a yet to be identified inhibitor(s). The acetone powder prepared from microsomes derived from livers of nutritionally normal cows contains vitamin K-dependent γ-glutamyl carboxylase. This enzyme can be solubilized from the powder using Triton X-100 and could provide a large supply of starting material for enzyme purification.