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є-N-Trimethyllysine Availability Regulates the Rate of Carnitine Biosynthesis in the Growing Rat

1986; Elsevier BV; Volume: 116; Issue: 5 Linguagem: Inglês

10.1093/jn/116.5.751

1541-6100

Charles J. Rebouche, Linda J. Lehman, Louise Olson,

Metabolomics and Mass Spectrometry Studies

Rates of carnitine biosynthesis in mammals depend on the availability of substrates and the activity of enzymes subserving the pathway. This study was undertaken to test the hypothesis that the availability of є-N-trimethyllysine is rate-limiting for synthesis of carnitine in the growing rat and to evaluate diet as a source of this precursor for carnitine biosynthesis. Rats apparently absorbed greater than 90% of a tracer dose of [methyl-3H]є-N-trimethyllysine, and approximately 30% of that was incorporated into tissues as [3H]carnitine. Rats given oral supplements of є-N-trimethyllysine (0.5–20 mg/d), but no dietary carnitine, excreted more carnitine than control animals receiving no dietary є-N-trimethyllysine or carnitine. Rates of carnitine excretion increased in a dose-dependent manner. Tissue and serum levels of carnitine also increased with dietary є-N-trimethyllysine supplementation. There was no evidence that the capacity for carnitine biosynthesis was saturated even at the highest level of oral є-N-trimethyllysine supplementation. Common dietary proteins (casein, soy protein and wheat gluten) were found to be poor sources of є-N-trimethyllysine for carnitine biosynthesis. The results of this study indicate that the availability of є-N-trimethyllysine limits the rate of carnitine biosynthesis in the growing rat.