INCREASED PLASMA PYRIDOXAL-5'-PHOSPHATE WHEN ALKALINE-PHOSPHATASE ACTIVITY IS REDUCED IN MODERATELY ZINC-DEFICIENT RATS

It is generally believed that the zinc metalloenzyme alkaline phosphat ase is required to hydrolyze phosphorylated forms of vitamin B-6 prior to their use. To test this hypothesis, rats were fed a liquid diet co ntaining either adequate or moderately low zinc during gestation and l actation. Zinc deficiency was produced in darns evidenced by significa nt reductions in zinc concentration of plasma (49%), liver (25%), and femur (24%), and plasma alkaline phosphatase activity (48%). Plasma py ridoxal-5'-phosphate (PLP), which significantly increased (61%) in the se same rats, was negatively correlated (r = -0.74, P < 0.02) with pla sma alkaline phosphatase activity. Maternal liver PLP concentration wa s unaffected by zinc status. The zinc and vitamin B-6 relationship see n in dams was less observable in offspring. Stimulation of erythrocyte alanine aminotransferase activity by exogenously added PLP in vitro t ended to be higher in both moderately zinc-deficient mothers and their offspring, but the difference was not significant. Our results suppor t the hypothesis that alkaline phosphatase activity is required for th e hydrolysis of plasma PLP. Our results also suggest that zinc status as alkaline phosphatase activity should be defined in an individual if plasma PLP is to be used as an indicator of vitamin B-6 status.