Table 2.

MTHFS catalyzed formation of the N5 iminium phosphate intermediate. The ability of MTHFS to catalyze formation of the N5 iminium phosphate was determined as described in Materials and Methods. Results shown as average and standard deviation of three experiments. The reaction buffer consisted of 100mM MES pH7.2, 10mM MgATP, 1mM phosphenolpyruvate, 200 μM NADPH, 3U/mL pyruvate kinase, 3U/mL lactate dehydrogenase, and 5U/ml C1 tetrahydrofolate synthase purified from rabbit liver. Activity is expressed as μM NADPH consumed per minute.

Substrate	[S] (μM)	Activity (μM/min)
5-formylTHF	10	0.99 ± 0.03
5-formylTHHF	10	0.05 ± 0.02
10-formylTHF	10	< 0.01
	80	< 0.01
5-formyl, 10-methylTHF	10	< 0.01
	80	< 0.01