Effect of Vitamin B6 Depletion in Adult Man on the Plasma Concentration and the Urinary Excretion of Free Amino Acids

Abstract

The effect of vitamin B₆ depletion on the plasma concentration and urinary excretion of free amino acids before and following a 3.00 g L-methionine loading dose was studied in six male college students fed an experimental diet which supplied 150 g protein and 0.16 mg vitamin B₆ daily. Vitamin B₆ depletion caused a substantial increase in both the fasting and 2-hour postprandial plasma concentration of glycine, serine and threonine, a marked increase in the pre- and postmethionine urinary excretion of serine and threonine and a slight increase in the postmethionine urinary excretion of glycine. During vitamin B₆ deprivation there also was a slight but significant decrease in the fasting plasma concentration of alanine, isoleucine, leucine and valine. Supplements of 2.00 mg pyridoxine daily to the subjects for 1 or 2 weeks caused the values to return to or approach predepletion levels.