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The Behavior of Muscle Phosphorylase as a Reservoir for Vitamin B₆ in the Rat¹

Department of Biochemistry, University of California, Berkeley, California

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.

KEY WORDS: • pyridoxal-p • muscle phosphorylase • starvation • vitamin B₆ deficiency • vitamin B₆ reservoir

¹ A preliminary report of this study was presented at a meeting of the Federation of American Societies for Experimental Biology; Federation Proceedings 26, 1170 (1977).

² On leave during this study from Department of Physiological Sciences, University of California, Davis 95616.

³ Current address: Department of Microbiology, University of Texas, Austin, Texas 78712.

Manuscript received 21 September 1977.