The Behavior of Muscle Phosphorylase as a Reservoir for Vitamin B6 in the Rat

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Abstract
Current belief that vitamin B6 deficiency causes depletion of muscle phosphorylase in animals appears to be erroneous. We present evidence that vitamin B6 deficiency is ineffective in reducing total phosphorylase in gastrocnemius muscle of young rats over a period of at least 8 weeks. Rats that had accumulated high levels of muscle phosphorylase while ingesting diets containing normal or excess amounts of the vitamin retained their phosphorylase after transfer to a vitamin B6 deficient diet. Prolonged deficiency did ultimately lead to enzyme depletion but this was after anorexia had developed and weight loss had occurred. When rats were partially starved for 1 to 4 days (fed 10% of normal energy intake) they lost muscle phosphorylase while retaining alanine and aspartate aminotransferases. When totally starved, the rats lost more phosphorylase than during partial starvation, but completely retained alanine aminotransferase, and lost some aspartate aminotransferase. We conclude that the behavior of muscle phosphorylase is consistent with the Krebs-Fischer proposal that it acts as a reservoir for vitamin B6 and that starvation, but not vitamin B6 deficiency per se, causes depletion of muscle phosphorylase. It appears that phosphorylase may function as an adjunct to adipose tissue necessary for the animal to efficiently meet the exigencies of starvation.