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Abstract Nicotinate phosphoribosyltransferase has been partially purified from bovine liver and some of its kinetic properties studied. This enzyme is easily separable from niacin ribonucleotidase. ATP is not a required substrate for bovine liver nicotinate phosphoribosyltransferase, as has been reported, but activates the enzyme by lowering the apparent Michaelis constants for both nicotinate and ribosylpyrophosphate 5-phosphate by approximately 10-fold. The stimulation by ATP appears to be highly specific. The kinetics of ATP activation indicate that ATP is binding at only one site on the enzyme. When ATP is present in the reaction, it is cleaved to form ADP in an amount approximately stoichiometric with nicotinic acid mononucleotide formation. It is suggested that ATP cleavage may be required for the activation of the enzyme.
Smith et al. (Wed,) studied this question.
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