Initial rate versus substrate concentration, [S], profiles (at pH 7.4, 37oC) for human jejunal glutathione disulfide reductase indicated partial substrate inhibition by GSSG at fixed [NADPH] \le 40 m M. Saturation by NADPH assumed an increasingly sigmoidal character at fixed [GSSG] \ge 20 m M. The results were interpreted in terms of a hybrid ping pong-semirandom mechanism proceeding through both E.NADPH (ping pong pathway) and E.GSSG (ordered pathway) complexes. When V(apparent) versus [GSSG] and [NADPH] were plotted, hyperbolic curves were obtained. Plotting 1/Vm(apparent) versus 1/[NADPH] and 1/[GSSG] yielded two lines with different slopes but intersecting at the same point on the y axis. A value of 26.3 U/ml was calculated for Vm, and Km values of 25 and 71 m M were determined for NADPH and GSSG, respectively.

Initial rate versus substrate concentration, [S], profiles (at pH 7.4, 37oC) for human jejunal glutathione disulfide reductase indicated partial substrate inhibition by GSSG at fixed [NADPH] \le 40 m M. Saturation by NADPH assumed an increasingly sigmoidal character at fixed [GSSG] \ge 20 m M. The results were interpreted in terms of a hybrid ping pong-semirandom mechanism proceeding through both E.NADPH (ping pong pathway) and E.GSSG (ordered pathway) complexes. When V(apparent) versus [GSSG] and [NADPH] were plotted, hyperbolic curves were obtained. Plotting 1/Vm(apparent) versus 1/[NADPH] and 1/[GSSG] yielded two lines with different slopes but intersecting at the same point on the y axis. A value of 26.3 U/ml was calculated for Vm, and Km values of 25 and 71 m M were determined for NADPH and GSSG, respectively.