( 2s,4r ) - '' '' erythro '' '' - and ( 2s,4s ) - '' '' threo '' '' -4-methylglutamic acids have been prepared by glutamate dehydrogenase-catalyzed reductive amination of 2-keto- ( r , s ) -4-methylglutaric acid , in the presence of nh4+ ions , nad+ , and a nadh recycling system ( ethanol-alcohol dehydrogenase ) , followed by separation by anion-exchange chromatography .
C0022023
h4+
C0003075
a