INCORPORATION OF THE HYDROGEN-ATOMS OF ETHANOL INTO AMINO-ACIDS IN RAT-LIVER INVIVO

Rats were injected intraperitoneally with [1-2H2]ethanol, (1R)-[1-2H]-ethanol, (1S)-[1-2H]ethanol or [2-2H3]ethanol. After different times, the rats were anesthetized and the liver was freeze-clamped in situ. Amino acids were isolated, converted into n-butyl ester N-trifluoroacetates and the labelling of alanine, proline, aspartate and glutamate was analyzed by gas chromatography-mass spectrometry. Aspartate became labelled during metabolism of [1-2H2]-ethanol, the deuterium excess in one position being 13 atoms% in samples isolated after 20 min of ethanol oxidation. Taken together with previous results on the labelling of malate this indicates that at least 60% of the liver aspartate was derived from oxaloacetate. About 24% of the transferred hydrogen was derived from the 1-pro-S position of the ethanol, indicating that both alcohol dehydrogenase and aldehyde dehydrogenase contribute NADH to malate dehydrogenase. Alanine and proline were labelled with deuterium after 4 h of [1-2H2]ethanol oxidation, the excess in one position being about 2 and 3 atoms%, respectively. Labelling of alanine indictates its formation from pyruvate derived from malate, and labelling of proline is explained by its formation in NAD(P)H-dependent reductions. All amino acids studied incorporated deuterium from [2-2H3]ethanol. The highest incorporation was observed in glutamate, and it was calculated that about 26% of the liver free glutamate was formed from ethanol after 4 h of ethanol oxidation. The presence of monodeuterated glutamate and proline molecules indicated exchanged of hydrogens at C-2 of ethanol during the incorporation. © 1979.