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Effect of Starvation in the Rat on Trimethyllysine in Peptide Linkage^1,2,

Veterans Administration Medical Center and Departments of Pharmacology and Medicine, Case Western Reserve University, School of Medicine, Cleveland, OH 44106

Trimethyllysine residues in peptide linkage, precursors of carnitine biosynthesis, were measured in fed and 3-day fasted rats. Whole-body peptide-linked trimethyllysine in fasted rats was significantly less than in fed rats when expressed per initial body weight (17.8 vs. 24.8 µmol/100 g initial body weight). Skeletal muscle had the highest peptide-linked trimethyllysine content (2.5 nmol/mg protein), followed by heart (1.9 nmol/mg protein). The content in kidney, liver and small intestine were similar, but less than in heart. Of the eight tissues tested, the brain had the only significant increase with fasting. The hepatic peptide-linked trimethyllysine in fasted rats was significantly decreased when expressed per milligram DNA. The study shows a commensurate loss of peptide-linked trimethyllysine accompanying protein loss during fasting. The study also shows that muscle contains over 65% of the whole-body peptide-linked trimethyllysine, and as such is a major reservoir of precursor for carnitine biosynthesis.

KEY WORDS: • trimethyllysine • carnitine biosynthesis • protein degradation

¹ Supported by National Institutes of Health grants AM-15804, 21009, and AM-07319, and the Medical Research Service of the Veterans Administration.

² Presented in part at the 72nd annual meeting of the American Society of Biological Chemists, St. Louis, MO, May 31–June 4, 1981. Fed. Proc. 40(6), 1685 (abs.).

³ To whom reprint request should be sent: Medical Research (151), Cleveland VA Medical Center, 10701 East Boulevard, Cleveland, OH 44106.

Manuscript received 1 November 1982.