• Journal of Nutrition and Health
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• v.25 no.6
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• pp.492-500
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• 1992

The rate of vitamin K-dependent carboxylation of endogenous liver microsomal proteins and an exogenous peptide substrate for carboxylase were measured to test the effects of excess vitamin A on vitamin K function in rats. In vitro vitamin A incubation in normal rat microsomes of vitamin K-sufficient ras did not influence the carboxylation rates of either endogenous prothrombin precursors or a peptide substrate added, Similarly vitamin A incubation in micro-somes from control and excess vitamin A-fed rats that were on vitamin K-free diet did not change the rate significantly within the respectively groups ; however the rates of endogenous protein carboxylation from excess vitamin A-fed rats tended to be increased by the in vitro vitamin A addition compared to that of control rats. Excess vitamin A-fed rats had 2- to 3- fold higher carboxylase activites of endogenous protein carboxylation either with or without the invitro vitamin A incubation than did control rats. In an in vivo study carboxyalase activites with an added exogenous peptide substrate were not influenced by excess intake of vitamin excess vitamin A-fed rats than for control rats. Carboxylase activites tended to be increased amounts of vitamin A on endogenous protein carboxylation appeareed as early as one week post-initiation of the diet. The results of this study indicate that excess vitamin A produces toxic effect rapidly and that excess dietary vitamin A increase the rate of carboxylation of endogenous protein mainly prothrombin precursors which is an indication of vitamin K defi-ciency.