(fos'fō-rī'bō-sil-glī-sin'ă-mīd sin'thĕ-tās), Glycinamide ribonucleotide synthetase; an enzyme that reacts glycine with ribosylamine 5-phosphate and ATP to form ADP, orthophosphate, and phosphoribosylglycineamide in the course of purine biosynthesis.