Two activities causing nitrite disappearance are found in extracts of Neurospora; one, inducible by nitrate or nitrite and present only in nitrite-utilizing strains, catalyze the stoichiometric reduction of nitrite to ammonia; the other, present in all strains under all conditions, causes the disappearance of nitrite to something other than ammonia. The latter activity has a molecular weight of about 600 and may contain an oligopeptide, a metal, and an SH group(s). It has no known physiological function.

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The effect of several organic solvents on the rate at which the carboxylesterases of beef liver hydrolyze u-nitrophenylbutyrate is reported. The organic solvents studied were acetone, methanol, ethanol, «propanol, 2-propanol, glycerol, dimethyl sulfoxide (DMSO), «-butanol, rec-butanol, rcrt-butanol, isobutanol, and «-pentanol. These solvents also affected the inhibition of liver enzymes by the pesticide Ruelene. A preliminary study of these effects was carried out at the 2.5% solvent concentration. This was followed by a more detailed study on acetone, methanol, glycerol, and DMSO at concentrations of up to 20%. The organic solvents were classified according to their effects on enzyme activation and inhibition: those which activated and decreased inhibition, those which deactivated and decreased inhibition, those which activated and increased inhibition, and those which deactivated and increased inhibition. The concentration of the solvent was a critical factor in enzyme activation and inhibition. The effects of these solvents on the optical properties of the reaction product, -nitrophenol, were also studied.

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