Effects of steroid and nonsteroid metabolites on enzyme conformation and pyridoxal phosphate binding.

Abstract

Studies on the effects of steroid and nonsteroid metabolites on enzy me conformation and pyridoxal phosphate binding were reviewed. The results indicate that conjugated steroids can cooperate with or oppose the actions of specific nonsteroid effectors in determining enzyme conformation activity stability and coenzyme binding. Evidence is presented that these actions of steroid and nonsteroid metabolites can cause a redistribution of pyridoxal phosphate between apoenzymes. It was considered that similar actions may account for the ability of estrogens to cause changes in tryptophan metabolism resembling those occurring during pyridoxine deficiency. Effects of estrogen-treatment and of dietary pyridoxine deficiency on the kynurenine transaminase levels in liver and kidneys of male rats were compared. Pyridoxine deficiency resulted in a moderate decline of the % saturation of the renal supernatant enzyme with pyridoxal phosphate but also caused an apparent decline in apoenzyme levels. Renal mitrochondrial apotransaminase levels decreased slightly during pyridoxine deficiency but were markedly decreased by estrogen treatment. Female rats displayed similar results to those of estrogen-treated males. These results indicate that the estrogens influence kynurenine transaminase in vivo in a way similar to that observed in vitro but also demonstrate that they do not cause the same pattern of change in apoenzyme levels and pyridoxal phosphate distribution as the dietary pyridoxine deficiency.