SUBSTRATE-SPECIFICITY OF GLYCINAMIDE RIBONUCLEOTIDE SYNTHETASE FROM CHICKEN LIVER

Several analogs of glycinamide ribonucleotide and phosphoribosylamine have been prepared and evaluated as substrates for glycinamide ribonuc leotide synthetase purified from chicken liver. Glycinamide ribonucleo tide analogs include side chain modifications wherein the glycine side chain (R = CH2NH2) has been replaced by R = CH2NHCH3 and R = CH2CH2NH 2, ribose ring replacement by chiral cyclopentane and cyclopentene der ivatives, and phosphate replacement by phosphonates. All of these, wit h the exception of the O-phosphonate, served as substrates for the rev erse enzymatic reaction, with V-max values comparable to that obtained with glycinamide ribonucleotide, although the K-m values ranged from 21 to 118 times the K-m for glycinamide ribonucleotide. Analogs of pho sphoribosylamine examined as substrates for the forward reaction consi st of chiral derivatives of cyclopentane and cyclopentene and a chiral carbocyclic phosphonate. These also served as substrates, with K-m va lues ranging from 5 to 23 times the K-m for phosphoribosylamine and wi th diminished V-max values. These studies have begun to define the str uctural features of the nucleotide substrate necessary to support enzy matic activity. Sarcosine (N-methylglycine) and beta-alanine were also accepted as substrates, albeit with reduced affinity compared with gl ycine.