R-5-P ATP PRPP合成酶 IMP的合成 IMP H20, PRPP FAICAR GIn 酰胺转移酶 HN CHO-FH4 PRA AICAR Gly ATP fumarate GAR R-5-P SAICAR CHO-FH4 Asp ATP ATP FGAR FGAM AIR C02 CAIRIMP的合成 R-5-P PRPP PRPP合成酶 PRA 酰胺转移酶 GAR FGAR FGAM AIR CAIR SAICAR AICAR FAICAR IMP Gln Gly Gln H2O CO2 Asp H2O ATP ATP ATP ATP HN N N N O R 5` P fumarate CHO-FH4 CHO-FH4