Table 1.

Kinetic parameters for the enzymatic ribosylation of purine analogues with various form of PNP as catalysts, and α-D-ribose-1-phosphate as a co-substrate. Data refer to pH 6.5.

Compound	Relative a kcat	Km [µM]	Enzyme source
2,6-diamino-8-azapurine	~0.4%	54	calf spleen
	2%	65	E. coli
2,6-diaminopurine b	<0.1%	-	calf spleen
	>120% c	~7	E. coli
8-azaguanine c	21%	100	calf spleen
	~4 U/mg	>200	E. coli

^a relative to those determined for guanine (=100%); ^b data from [15], at pH 7; ^c relative to the parameters determined for N7-methylguanosine phosphorolysis at pH 6.5 (=100).