Photoinactivation and photoreactivation of constitutive and adaptive respiratory systems of Azotobacter.

Acetate grown cells of Azotobacter, like sucrose grown cells (Stone and Wilson, 1952), are unadapted to the oxidation of succinic acid although possessing an enzyme system capable of oxidizing succinate. Hence the adaptation of these cells to succinic acid may be termed a functional change in the physiology of the organism. In contrast, glucose grown cells of Saccharomyces cerevisae are unadapted to the fermentation of galactose and do not possess an enzyme system capable of fermenting this sugar. Adaptation to galactose fermentation corresponds with the appearance within the yeast cell of an apoenzyme capable of fermenting galactose (Spiegelman, 1950). The adaptation of glucose grown celLs of Saccharomyces cerevias to galactose represents, therefore, an organic change in the enzyme component of the cell. Functional and organic adaptation processes may be inhibited by doses of ultraviolet light, which have but a negligible effect on the activity of constitutive and adaptive respiratory enzymes (Stephenson and Yudkin, 1936; Barrett et al., 1953). The inhibition of organic adaptive process by ultraviolet light has been shown to be abolished in yeast (Swenson and Giese, 1950) by exposing the ultraviolet irradiated cells to visible light (Kelner, 1949). This study deals with the inhibitory effect of ultraviolet light on adaptive and constitutive respiratory systems of a bacterium and the reversal of this effect by visible light.