COARSE AND FINE CONTROL AND ANNUAL CHANGES OF SUCROSE-PHOSPHATE SYNTHASE IN NORWAY SPRUCE NEEDLES

Annual changes of activity of sucrose-phosphate synthase (SPS) from sp ruce (Picea abies [L.] Karst.) needles were studied with respect to th ree regulatory levels: metabolic fine control, covalent modification ( phosphorylation), and protein amount. Glucose-6-phosphate served as an allosteric activator of spruce SPS by shifting the Michaelis constant for the substrate fructose-6-phosphate from 4.2 to 0.59 mM, whereas i norganic phosphate competitively inhibited this activation. The affini ty for the other substrate, UDP-glucose, was unaffected. Incubation of the crude extract with ATP resulted in a time- and concentration-depe ndent decrease of the maximal velocity of SPS. This inactivation was s ensitive to staurosporine, a potent protein kinase inhibitor, indicati ng the participation of a protein kinase. Probing SPS protein with het erologous antibodies showed that the subunit of spruce SPS is an appro ximately 139-kD protein and that changes in the extractable activity d uring the course of a year were correlated with the amount of SPS prot ein. High SPS activities in winter were paralleled by increased levels of the activator glucose-6-phosphate and the substrate fructose-6-pho sphate, indicating a high capacity for sucrose synthesis that may be n ecessary to maintain photosynthetic CO2 fixation in cold-hardened spru ce needles.