Table I.

PRPP synthase activity specified by PRS1, PRS2, PRS3, and PRS4 cDNAs

Isozyme	Pia	Specific Activityb
		−ADP	+ADP
		nmol min−1 mg−1 protein
1	+	191	74
	−	14	NDc
2	+	140	18
	−	25	ND
3	+	1060	880
	−	1260	884
4	+	80	72
	−	89	99

PRPP synthase activity was determined as described in Methods. Values are the averages of five determinations.

^a+, Activity assayed in the presence of 50 mm Pi; −, no Pi present. 

^b−ADP, Activity determined by the standard assay in the presence of 1.0 mm ATP; +ADP, activity assayed in the presence of 1.0 mm ADP and 1.0 mm ATP. 

^cND, Not determined.