Table V.

AtSEX4-mediated hydrolysis of C6 and C3 phosphate esters at native starch granules

Native sex1-3 starch granules were prelabeled with ³³P at either C6 or C3 positions and were then incubated with AtSEX4 (see “Materials and Methods”). The released radioactive label was quantified by scintillation counting. Phosphatase activity is given as specific enzyme activity (nmol P mg⁻¹ SEX4 min⁻¹) or as the relative rate of ³³P release in the reaction mixture; the total ³³P content of the starch added to the reaction mixture is taken as 100% (% P min⁻¹). Mean values ±se are given (n = 3).

Position of 33P-Labeled Phosphate	Phosphate Content	Phosphatase Activity
	pmol P mg−1 starch	nmol P mg−1 SEX4 min−1	% P min−1
C6	90.169	3.675 ± 0.037	0.509 ± 0.005
C3	32.615	0.643 ± 0.012	0.247 ± 0.005