Sucrose Synthase, a Cytosolic Enzyme in Protoplasts of Jerusalem Artichoke Tubers (Helianthus tuberosus L.).

The exact subcellular location of sucrose synthase (UDP-d-glucose: d-fructose 2-alpha-d-glucosyltransferase, EC 2.4.1.13) in Helianthus tuberosus tubers was studied by comparison of its activity in protoplasts with that of vacuoles isolated from them. Assuming 100% of the beta-N-acetylglucosaminidase activity to be of vacuolar origin, less than 5% of both the sucrose synthase activity and the extravacuolar marker NAD-malate dehydrogenase was detected in the vacuole preparations. Sucrose synthase is therefore an extravacuolar enzyme. Its role in the inulin metabolism of H. tuberosus is discussed.