Final answer:
The synthesis of GMP from guanine and PRPP by the PRPP salvage reaction requires just one high-energy phosphate bond equivalent, which comes from the hydrolysis of PRPP.
Step-by-step explanation:
The synthesis of GMP from guanine and PRPP by the PRPP salvage reaction in purine metabolism requires the use of high-energy phosphate bond equivalents. PRPP (phosphoribosyl pyrophosphate) stands for 5-phosphoribosyl 1-pyrophosphate, which already contains high-energy bonds. When guanine reacts with PRPP, catalyzed by the enzyme Hypoxanthine-guanine phosphoribosyltransferase (HGPRT), GMP (guanosine monophosphate) is formed.
The conversion of guanine to GMP through the salvage pathway requires the cleavage of the pyrophosphate bond in PRPP. This process expends one high-energy phosphate bond equivalent, as PRPP is converted to ribose-5-phosphate plus the guanine moiety is added, forming GMP. It is important to note that no additional ATP or GTP hydrolysis is required in this salvage reaction, so the total cost is one high-energy phosphate bond equivalent, which comes from the hydrolysis of PRPP.