Loss of in vitro inactivation of rat liver tyrosine aminotransferase with dietary vitamin B6 restriction.
Tyrosine aminotransferase, in the presence of 8 mM L-cysteine, is inactivated in incubated liver homogenates prepared from normal rats, but not in those from rats deprived of vitamin B6. In this study we fed rats a diet deficient in vitamin B6 to determine the length of time required for in vitro inactivating activity to be lost from liver homogenates. After 2 weeks, the half-life of tyrosine aminotransferase in liver homogenates from vitamin B6-deficient rats was 5.9 hours, and from control rats, 1.8 hours. After 3 weeks, tyrosine aminotransferase was no longer inactivated in homogenates prepared from livers of deficient rats. The pyridoxal phosphate (PLP) concentration of plasma from rats fed the vitamin B6-deficient diet dropped from 89 ng/ml to 14 ng/ml after 1 week and to 7 ng/ml after 2 weeks. In 5 weeks the PLP concentration of liver from vitamin B6-adequate rats increased from 2.9 microgram/g to 6.6 microgram/g while in deficient rats it dropped to 2 microgram/g. The loss of tyrosine aminotransferase inactivating activity in the livers of vitamin B6-deficient rats occurred at approximately the same time that the concentration of PLP in the livers of rats fed the two diets began to show marked differences.
Loss of in vitro inactivation of rat liver tyrosine aminotransferase with dietary vitamin B6 restriction. Tyrosine aminotransferase, in the presence of 8 mM L-cysteine, is inactivated in incubated liver homogenates prepared from normal rats, but not in those from rats deprived of vitamin B6. In this study we fed rats a diet deficient in vitamin B6 to determine the length of time required for in vitro inactivating activity to be lost from liver homogenates. After 2 weeks, the half-life of tyrosine aminotransferase in liver homogenates from vitamin B6-deficient rats was 5.9 hours, and from control rats, 1.8 hours. After 3 weeks, tyrosine aminotransferase was no longer inactivated in homogenates prepared from livers of deficient rats. The pyridoxal phosphate (PLP) concentration of plasma from rats fed the vitamin B6-deficient diet dropped from 89 ng/ml to 14 ng/ml after 1 week and to 7 ng/ml after 2 weeks. In 5 weeks the PLP concentration of liver from vitamin B6-adequate rats increased from 2.9 microgram/g to 6.6 microgram/g while in deficient rats it dropped to 2 microgram/g. The loss of tyrosine aminotransferase inactivating activity in the livers of vitamin B6-deficient rats occurred at approximately the same time that the concentration of PLP in the livers of rats fed the two diets began to show marked differences.