In vitro and in situ studies on the inhibition of yeast AMP deaminase by fatty acids.

The effect of various fatty acids on the purified and in situ AMP deaminase (AMP aminohydrolase, EC 3.5.4.6) was investigated: both the purified AMP deaminase and the permeabilized system of yeast cells were used as the enzyme sources. (1) All the saturated fatty acids, longer than 10 in the hydrocarbon chain, were inhibitors of the purified enzyme in the absence of ATP, whereas no or little inhibition of the enzyme was observed in the presence of ATP. Unsaturated fatty acids acted as more potent inhibitors of the purified enzyme, although the addition of ATP increased the I0.5 values for these fatty acids. Fatty acids acted as non-competitive inhibitors without alteration of the affinity for the substrate in the absence and presence of ATP. (2) Unsaturated fatty acids showed a powerful inhibition of the in situ AMP deaminase, and the presence of ATP could scarcely affect the inhibition of the in situ enzyme by these fatty acids. On the other hand, no or little inhibition of the in situ enzyme by saturated fatty acids was observed in the absence and presence of ATP. The difference in the kinetics properties between the in situ and the purified enzyme suggests that there is difference in protein interactions for AMP deaminase in situ and in vitro.