Enzyme assay for the rapid determination of plasma lysine

Abstract

The enzymic determination of lysine, using saccharopine dehydrogenase, has been modified to determine plasma lysine concentrations in approximately 5 min. The correlation between lysine concentration determined by using HPLC and this enzymic assay was high (r²= 0.92). The main interfering compound was leucine which, at 250 µmol l^–1, inhibited the rate measured with lysine by 17%. One application of this method allows plasma lysine to be ‘clamped’ under hyperinsulinemic euglycemic conditions. The technique may be applicable to the bedside investigation of the roles of hormones and nutrition in the regulation of protein metabolism.