The Effect of Glycerol in the Storage Medium on the Inhibitory Kinetic Behavior of Glutathione Reductase

Abstract

In this study we report on the effect of glycerol used in storage buffers, on the inhibitory kinetic behavior of NADP(+) on rat kidney glutathione reductase (rkGR) stored at -80 degrees C in +/- 10% (v/v) glycerol. At fixed [GSSG] and varied [NADPH], rkGR stored +/- glycerol were inhibited competitively by NADP(+). Although the addition of glycerol decreased K-m (9.7 +/- 0.9 mu M) and Ki(NADp+) (26.6 +/- 2.2 mu M) for NADPH, the catalytic efficiency (K-cat/K-m = 2.75 x 10(7) M-1.s(-1)) was increased 1.64 fold. At fixed [NADPH] and varied [GSSG], rkGR exhibited noncompetitive (K-i = 397 69 mu M) and linear mixed-type (K-i = 59.6 +/- 8.4 mu M; K-s = 49.9 +/- 3.2 mu M; alpha = 7.74) inhibitions with and without glycerol during storage. The K-cat/K-m of rkGR stored in glycerol was 5.16 x 10(6) M-1.s(-1). Although the increase in K-cat was 1.25 fold, the K-cat/K-m was minimally affected (1.06).