Measurement of enzymes related to sucrose metabolism in permeabilized Chlorella vulgaris cells

Sucrose phosphate synthase (UDP-glucose: D-fructose-6-phosphate-2-glucosyl transferase, EC 2.4.1.14), sucrose synthase (UDP-glucose: D-fructose-2-glucosyl transferase, EC 2.4.1.13) and invertase (β-D-fructofuranoside fructohydrolase, EC 3.2.1.26) were measured in toluene permeabilized cells of Chlorella vulgaris Beijerinck. All three activities were detected at all stages of the growth curve; sucrose synthase and sucrose phosphate synthase showed a zone of maximum activity, while invertase increased with time of growth. Sucrose phosphate synthase and sucrose synthase (sucrose synthesis direction) were stimulated by divalent cations and inhibited by UDP. This inhibition could be reversed by Mg²⁺ or Mn²⁺. Sucrose phosphate synthase activity was inhibited by inorganic phosphate and was enhanced by glucose-6-phosphate, but was insensitive to sucrose. Arbutine decreased sucrose synthase activity in both directions. Sucrose cleavage was inhibited by divalent cations and by pyrophosphate. The effects on the enzyme activities of the presence of 2,4-dichlorophenoxyacetic acid (2,4-D), gibberellic acid, abscisic acid and kinetin in the growth medium were investigated. Sucrose synthase activity was practically unaffected by all plant hormones tested, except for the presence of kinetin which stimulated the activity. Sucrose phosphate synthase activity was increased by both kinetin and abscisic acid. The effect of the latter was partially reversed by the presence of gibberellic acid. 2,4-D and kinetin were potent stimulators of invertase activity.