Some Esterases of Cows’ Milk

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Abstract
Comparisons of the in-hibitory action of various concentrations (10-7 to 10-2 [image]) of the organophosphorus compounds, N, N1-diisopropyl phosphor diamido-fluoridate (Isopestox), diethyl p-nitrophenyl thiophosphate (Parathion), diisopropyl fluorophosphate (DFP), and tetraethyl pyrophosphate (TEPP) on the activity of milk enzymes toward a variety of pure esters of 17-fatty acids has led to the differentiation of 3 esterases or esterase systems. One, a typical arylesterase (A-esterase), was responsible for about 80%, of the activity of milk enzymes toward phenyl acetate and was not inhibited by 10-2 [image] concentrations of any of the inhibitors used. A 2d, an aliphatic esterase (B-esterase), was responsible for about 95%, of the observed hydrolysis of tributyrin. It was not inhibited by 10-2 [image] Isopestox but was completely inhibited by this concentration of Parathion, DFP, or TEPP. The 3d esterase, which may be a cholinesterase, was completely inhibited by 10-6 [image] concentrations of DFP or TEPP. It was responsible for about 70% of the activity of milk enzymes toward phenyl propionate.