A phosphoribosyl-enzyme covalent intermediate in the first enzyme of histidine biosynthesis

Abstract

Evidence is presented that the mechanism of phosphoribosyl-adenosine triphosphate: pyrophosphate phosphoribosyltransferase (the first enzyme of histidine biosynthesis) proceeds through a covalent phosphoribosyl-enzyme intermediate. The intermediate has been demonstrated after incubating the enzyme with 14C-PRPP under both “native” and denaturing conditions. The intermediate also forms from the reverse direction as demonstrated by an initial burst phenomenon when the enzyme is mixed with its product, PR-ATP. Thus, exchange data coupled with specificity requirements appears to provide sound evidence for a covalent enzyme-substrate intermediate.