Effect of histidine on respiration.

E. coli and S. aureus were grown to mid-log phase with 5.0 mM histidine (His) or without histidine. The cells were washed and resuspended to OD = 0.5 in PBS/glucose. Half ml of cell suspension was added to 2.5 ml of PBS glucose in a thermostatic chamber fitted with a Clark electrode. In separate runs, histidine was added to non-treated cell suspensions to a final concentration of 5.0 mM (the third set of bars). The experiment was repeated twice in triplicates. Mean ± SD is presented.