Table II.

Activation of wild-type and mutant maize endosperm AGPase by allosteric effectors

Activities in the presence of F-6-P and G-6-P are approximately 60% to 80% of what is observed with 3-PGA for all enzymes.

Enzyme	Mutant Subunit	A50
		3-PGA	F-6-P	G-6-P
		mm
Wild type	–	0.22 ± 0.03	0.6 ± 0.1	4.0 ± 0.8
R104A	Large	7 ± 1a 4 ± 1b	6 ± 2a 0.9 ± 0.2b	19 ± 4a 5 ± 1b
R77K	Small	4.3c	65 ± 20	N.D.d
R116A	Large	0.8 ± 0.2	1.4 ± 0.1	6.2 ± 0.9
R107A	Small	1.2 ± 0.3	0.30 ± 0.07	2.1 ± 0.8
R146A	Large	1.5 ± 0.4	2.7 ± 0.5	6 ± 3
R340A	Small	3.5 ± 0.7	7 ± 2	18 ± 3
R381A	Large	2.0 ± 0.5	3.2 ± 0.4	13 ± 3

^aActivity was determined in the presence of 1 mm ATP.

^bActivity was determined in the presence of 6 mm ATP.

^c3-PGA inhibits the R77K mutant at concentrations above 10 to 15 mm.

^dNot determined (N.D.) since activity increased linearly with increasing [G-6-P] up to 50 mm.