Purine Biosynthesis De Novo in the Bovine Retina: Purification and Characterization of the Amidophosphoribosyl Transferase and Phosphoribosyl Pyrophosphate Synthetase

摘要

Ability of bovine retina to synthesize purines de novo is shown for the first time. Amidophosphoribosyl transferase the enzyme controlling the rate of the pathway, and phosphoribosyl pyrophosphate synthetase, the enzyme regulating the intracellular contents of phosphoribosyl pyrophosphate, were purified and characterized. Molecular weight of enzyme subunits are similar to those of the purified enzyme from the liver. Molecular weights of amidophosphoribosyl transferase, PRPP synthase catallytic subunit, and two PRPP synthaseassociated proteins were 50, 34, 39 and 41 kD, respectively. Apparent K_m of the enzymes are similar to that of the purified enzyme from the liver. In case of amidophosphoribosyl transferase, apparent K_m for Gln and PRPPwere 0.75+-0.05 and 0.66+-0.09 mM, respectively. In case of PRPP synthase, apparent K_m for ribose-5-phosphate and ATP were 37.9+-0.5 and 53+-7#mu#M. The sensitivity of the retinal PRPP synthetase to inhibition by ADP was significantly lower than that of the enzyme from the liver