Abstract
SUMMARY
Studies of the nature of the inhibitory action of inorganic phosphate, fluoride, and some detergents on 5’-adenylic acid deaminase activities of rat brain and liver show that inorganic phosphate, as well as ATP, is an effector of the deaminase.
Inorganic phosphate was found to be a competitive inhibitor in the absence of ATP, but in the presence of ATP, the na- ture of the inhibition was uncompetitive. ATP strongly prevented the inhibition by inorganic phosphate. It appears that inorganic phosphate competes with the substrate, AMP, and with the activator, ATP, simultaneously at the active site and the effector site, respectively.
Fluoride inhibited the deaminase noncompetitively in the absence of ATP, and uncompetitive effect was obtained in the presence of ATP. It is likely that fluoride competes with ATP in binding to the effector binding site, and in the absence of ATP fluoride occupies the effector binding site to modify the activity.
Deoxycholate and lauryl sulfate acted as activators or in- hibitors, depending upon the enzyme concentrations and the inhibitor concentrations. The inhibition was also dependent upon the substrate concentrations and therefore showed a mixed type in nature. ATP could prevent the inhibitory effect, but higher deoxycholate concentrations reduced or diminished the ATP-activated activity. It appears that deoxycholate or lauryl sulfate can affect the ATP-binding site in modifying the ATP-activation as well as the deamination.
The physiological significance of the relationship between inorganic phosphate and ATP in regard to AMP metabolism and consequently to intermediary metabolism is discussed.