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 PhosphatePhosphate ContentPhosphatase Activity
pmol P mg−1 starchnmol P mg−1 SEX4 min−1% P min−1
C690.1693.675 ± 0.0370.509 ± 0.005
C332.6150.643 ± 0.0120.247 ± 0.005