Synthesis of clotting factors by a cell-free system from rat liver in response to the addition of vitamin K 1 in vitro

Abstract

A cell free system from the liver of vitamin K-deficient rats will form clotting factors after addition of vitamin K 1 in vitro. The response requires both microsomal pellet and supernatant. It is not energy dependent and no co-factor requirement could be demonstrated. Immunological tests and the response to vitamin K 1 analogues demonstrate the physiological nature of the response. It has been recently claimed that vitamin K is required for the formation of calcium binding sites by carboxylation of glutamyl residues. Failure to demonstrate an energy requirement in this system suggests that either vitamin K-dependent carboxylation proceeds by a mechanism hitherto unknown in biology or that the vitamin K-dependent reaction is not directly coupled to carboxylation.