NADH oxidase activity of soybean plasma membranes oscillates with a temperature compensated period of 24 min

The enzymatic activity of a hormone-stimulated and growth-related protein d isulfide-thiol oxidoreductase (NADH oxidase) with protein disulfide-thiol i nterchange activity of etiolated hypocotyls of soybean oscillates with a pe riod of about 24 min or 60 times per 24 h day. The oscillations were temper ature compensated such that the period remained constant at about 24 min be tween 17 and 37 degrees C, a temperature range over which enzymatic activit y varied approximately fourfold (Q(10) of 2). The oscillations were observe d with intact tissue sections, with isolated plasma membrane vesicles, and with the detergent-solubilized and partially purified enzyme. The oscillati ons were observed both with the oxidation of NADH and in the restoration of activity to scrambled ribonuclease used as a measure of the protein disulf ide-thiol interchange activity. The enzymatic activity which is located at the cell surface may represent a biochemical reaction with a potential func tion as an ultradian oscillator of circadian time keeping.