Pyridoxine-beta-glucoside (PNG) is a major component of vitamin B6 (B6) in plant foods, and PNG hydrolysis catalyzed by PNG hydrolase is rate limiting for the in vivo utilization. The applicant showed that PNG is approximately 50% bioavailable in relation to free pyridoxine in humans. PNG hydrolase and """"""""broad specificity beta-glucosidase (BSBG)"""""""" activities are inversely proportional to B6 nutriture. The applicant hypothesized that regulatory mechanism of these enzymes involves either an effect of intracellular pyridoxal phosphate or changes in S-adenosylmethionine levels that are controlled by B6 and folate nutriture. The applicant also hypothesized that increased PNG hydrolase activity contributes to an increased PNG bioavailability in B6-deficient humans and compensates for the deficiency. The applicant will: 1) develop antibodies to intestinal BSBG and PNG hydrolase to measure the abundance of each enzyme; 2) clone the cDNAs for intestinal BSBG and PNG hydrolase and quantitate mRNAs; 3) evaluate in rats the effect of B6 deficiency, repletion and excess on the activity, enzyme mass, and mRNA abundance of PNG hydrolase and BSBG, and evaluate the effect of folate deficiency on enzyme regulation; and 4) determine the extent to which PNG hydrolase activity is influenced by B6 status in humans using deuterium-labeled PNG. These studies will provide new insight into the regulation of PNG hydrolase that is the rate-limiting enzyme for the utilization of glycosylated B6 in human diets.
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