ε-N-Methyl Lysine: an Additional Amino-acid in Human Plasma

Abstract

WE have found that plasma of fasting humans usually contains small amounts of a previously unrecognized ammo-acid which we have tentatively identified as ε-N-methyl lysine. We first noted the presence of this compound when we began chromatographing plasma samples from adults with a new automatic amino-acid analyser technique¹, which uses an elution gradient of lithium citrate buffers instead of the usual sodium citrate buffers. Our procedure alters the order of emergence of certain amino-acids from the column, and we were surprised to observe the regular appearance on chromatograms of a small unidentified peak between lysine and histidine. 1-Methyl histidine, 3-methyl histidine and the dipeptides anserine and carnosine are all eluted after histidine with our technique, and no known ninhydrin-positive components of plasma should have been eluted between lysine and histidine.