A procedure for the assay of sucrose synthetase and sucrose phosphate synthetase in plant homogenates

The determination of these two enzymic activities is commonly based on the destruction of remaining fructose or fructose-6-P by treatment with borohydride or alkali (1,2,4). These methods are quite suitable for kinetic determinations, but they are not adequate for testing the enzymes in crude homogenates from various plant tissues. In this case, methods which measure the formation of [14C]sucrose from UDP-[14C]glu cose have been used. Radioactive sucrose is separated from the labeled substrate by paper electrophoresis (5) or by paper chromatography (6). Similarly, the labeled sucrose phosphate in the reaction catalyzed by sucrose phosphate synthetase is separated from the substrate by paper chromatography after submitting the ester to the action of alkaline phosphatase (7). In the latter case a similar technique is applied if radioactive fructose-6-P is used instead of UDP-glucose (7). Thus, these procedures, even if they give reproducible results, are