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Increased Muscle Phosphorylase in Rats Fed High Levels of Vitamin B₆¹

Department of Biochemistry, University of California, Berkeley, California 94720

The present study was undertaken to test the hypothesis that muscle phosphorylase may function as a repository for vitamin B₆ in the animal. Since a repository would be expected to accumulate surplus material, one would predict that phosphorylase, which contains stoichiometric amounts of pyridoxal phosphate, would increase in muscle of animals surfeited with the vitamin. Rats were fed a vitamin B₆-free diet supplemented with pyridoxine providing levels 10, 1.0 and 0.1 of those recommended by the National Research Council (NRC). At the high intake level, muscle phosphorylase and total muscle vitamin B₆ increased steadily and in almost constant ratio for at least 6 weeks, whereas both alanine and aspartate transaminase increased initially, but reached a plateau within 2 weeks. At the intermediate level of pyridoxine intake, muscle phosphorylase also increased, but less rapidly than in rats fed the higher level. When vitamin B₆ intake was restricted to 10% of the NRC-recommended level, no increase in phosphorylase concentration occurred during a period of 10 weeks. These results support the hypothesis that muscle phosphorylase acts as a reservoir for vitamin B₆ in the animal and provide experimental evidence that muscle enzyme content expands as vitamin is accumulated during high dietary intake.

KEY WORDS: • vitamin B₆ • muscle phosphorylase • vitamin reservoir

¹ This study was supported in part by NIH grants #AM 01448 and #AI 01575.

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

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

Manuscript received 28 April 1977.