Abstract Histidine and its analogs were demonstrated to activate crystalline beef liver glutamate dehydrogenase ( l -glutamate: NAD+ oxidoreductase (deaminating), EC 1.4.1.2). Activation effects were similar to those of other amino acids such as leucine or norvaline, which have been shown previously by others to exert their activating effect with respect to high concentration and in which kinetic studies also revealed modified values for both K m and ν max . Unlike ADP, histidine did not alter the fluorescence intensity caused by enzyme-coenzyme binding but increased the sedimentation coefficient of the enzyme slightly in either the native or disaggregated state by NADH.