L-histidine ammonia-lyase from a T-strain Mycoplasma (Ureaplasma urealyticum).

L-histidine ammonia-lyase (E.C. 4.3.1.3) activity was shown to occur in cell-free extracts of Ureaplasma urealyticum. The activity of the crude enzyme depends on the presence of thiol compounds. However, higher than optimal concentrations of reduced glutathione, were shown to cause some inhibition of enzyme activity. This enzymatic reaction is characterized by a "lag" phase, whose duration depends on assay conditions. The substrate saturation curve shows a sigmoidal pattern probably due to the presence (in crude enzyme preparations) of some inhibiting impurity which reversibly combines with the substrate. Statistically significant increases of enzyme activity were demonstrated in crude enzyme preparations obtained from mycoplasma cells grown in broth medium supplemented with 16 mM L-histidine.