Comparison of alanine production after L-leucine and AMP deamination in an enzymatic model and in muscle specimens.

The amination of 2-oxoglutarate to glutamate by the deamination of leucine followed by the transamination of pyruvate to alanine in skeletal muscle is generally accepted. However, alanine formation following AMP deamination by AMP deaminase is still questionable even though it is theoretically possible. For this reason, we investigated in an enzymatic model the dependence of alanine yield both on the increasing concentration of AMP and leucine as amino group donors as well as on AMP deaminase and leucine dehydrogenase augmentation. Up to a concentration of 375 microM neither of the amino group donors produced a difference in the glutamate nor alanine yield. At a concentration of 500 microM ammonia formation was less, but alanine production was higher when leucine was present as a starting material. However, in muscle samples obtained from trained or untrained rats we did not find an increase in alanine yield when AMP was added to the muscle sample, even though NH3 production was significantly higher in samples with than in those without AMP. This discrepancy might be further elucidated by hindquarter perfusion experiments, in which alanine release would be determined after AMP deamination enhanced by electrostimulation of these muscle groups.