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.
D000818:Animals; D001835:Body Weight; D006207:Half-Life; D008099:Liver / Q000378:metabolism*; D008297:Male; D011732:Pyridoxal Phosphate / Q000097:blood / Q000378:metabolism*; D051381:Rats; D014444:Tyrosine Transaminase / Q000037:antagonists & inhibitors*; D026681:Vitamin B 6 Deficiency / Q000201:enzymology*
D011732:Pyridoxal Phosphate; D014444:Tyrosine Transaminase