JBC, Vol. 250, Issue 17, 6885-6890, Sep, 1975
Evidence against a covalent intermediate in the adenosine triphosphate phosphoribosyltransferase reaction of histidine biosynthesis
W. T. Brashear and S. M. Parsons
14C-Labeled 5-phospho-alpha-D-ribose-1-diphosphate (PRibPP) was synthesized
and its interaction with adenosine triphosphate phosphoribosyltransferase
was examined by gel filtration in a search for a form of this substrate
covalently bound to the enzyme. Wide variation in solvent conditions gave
little labeling of the enzyme. Heavy labeling was found only in the
presence of the second substrate, ATP, and this was shown to arise from
tightly but noncovalently bound product. Previous reports of a covalent
intermediate in this enzymatic reaction probably were due to contaminating
ATP in 5-phospho-alpha-D-ribose-1-diphosphate. Feedback inhibition of the
enzyme by histidine was shown to occur at the step giving product or at
some earlier step in the mechanism.