[Self-inactivation of NADH-oxidase from Mycoplasma cells during reaction]

The feasibility of self-inactivation of NADH-oxidase by plasma membranes of Acholeplasma laidlawii cells was investigated. It was demonstrated that the rate of NADH oxidation in a flow reactor upon stirring diminishes with time. This decrease of the reaction rate is not coupled with the presence in the reaction mixture of the reaction products--NAD+ and H2O2, and is irreversible. In the absence of NADH the enzyme activity is unaffected. The data obtained suggest that NADH-oxidase is inactivated in the course of the catalytic reaction. Under the stipulation that the enzyme obtained from plasma membranes of aged (60 hrs of inoculation) cells has identical values of Km and ki but lower values as compared to young cells (24 hrs of inoculation) of Vmax and v0, it is concluded that the decrease of the NADH-oxidase activity upon ageing of cultures is due to the decrease in the amount of active molecules of AND-oxidase in mycoplasm cell plasma membranes.