Where does N(ε)-trimethyllysine for the carnitine biosynthesis in mammals come from?
N(ε)-trimethyllysine (TML) is a non-protein amino acid which takes part in the biosynthesis of carnitine. In mammals, the breakdown of endogenous proteins containing TML residues is recognized as starting point for the carnitine biosynthesis. Here, we document that one of the main sources of TML could be the vegetables which represent an important part of daily alimentation for most mammals. A HPLC-ESI-MS/MS method, which we previously developed for the analysis of N(G)-methylarginines, was utilized to quantitate TML in numerous vegetables. We report that TML, believed to be rather rare in plants as free amino acid, is, instead, ubiquitous in them and at not negligible levels. The occurrence of TML has been also confirmed in some vegetables by a HPLC method with fluorescence detection. Our results establish that TML can be introduced as free amino acid in conspicuous amounts from vegetables. The current opinion is that mammals utilize the breakdown of their endogenous proteins containing TML residues as starting point for carnitine biosynthesis. However, our finding raises the question of whether a tortuous and energy expensive route as the one of TML formation from the breakdown of endogenous proteins is really preferred when the substance is so easily available in vegetable foods. On the basis of this result, it must be taken into account that in mammals TML might be mainly introduced by diet. However, when the alimentary intake becomes insufficient, as during starvation, it might be supplied by endogenous protein breakdown.
Department of Biochemistry, Biophysics and General Pathology, Second University of Naples, Naples, Italy.
Luigi
L
Servillo
Department of Biochemistry, Biophysics and General Pathology, Second University of Naples, Naples, Italy.
Alfonso
A
Giovane
Stazione Sperimentale per le Industrie delle Essenze e dei Derivati dagli Agrumi (SSEA), Reggio Calabria, Italy.
Domenico
D
Cautela
Dipartimento di Ingegneria Industriale e ProdAl scarl, Università degli Studi di Salerno, Fisciano (SA), Italy.
Domenico
D
Castaldo
Department of Biochemistry, Biophysics and General Pathology, Second University of Naples, Naples, Italy.
Maria Luisa
ML
Balestrieri
D000818:Animals; D053898:Biosynthetic Pathways; D002331:Carnitine / Q000096:biosynthesis*; D002853:Chromatography, Liquid; D056148:Chromatography, Reverse-Phase; D005453:Fluorescence; D008239:Lysine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D008322:Mammals / Q000378:metabolism*; D010936:Plant Extracts / Q000737:chemistry; D021241:Spectrometry, Mass, Electrospray Ionization; D014675:Vegetables / Q000737:chemistry
D010936:Plant Extracts; C003712:trimethyllysine; D008239:Lysine; D002331:Carnitine