Abstract
Sucrose-phosphate synthase (SPS) from mature apple (Malus domestica Borhk. cv. Gala) leaves was purified 34-fold to a final specific activity of 15.3 μmol mg-1 protein h-1. The enzyme showed hyperbolic saturation kinetics for both fructose-6-phosphate (F6P) (Km= 0.36 mM) and uridine-5'-diphosphoglucose (UDPG) (Km = 6.49 mM). Glucose-6-phosphate (G6P) was found to be an activator of apple SPS, and the activation was dependent upon the F6P concentration. At a concentration of 2 mM, G6P significantly decreased the Km for F6P and increased SPS activity. However, higher concentrations of G6P did not further stimulate SPS activity. In contrast to SPS from other plant species, inorganic phosphate (Pi) had little or no inhibitory effect on apple SPS. The apple leaf enzyme was inhibited 7-10% by 10 mM Pi when F6P concentrations were in the range of 2-10 mM. We observed that sorbitol-6-phosphate, an intermediate metabolite in sorbitol biosynthesis, was a competitive inhibitor of SPS with a Ki of 1.83 mM. Sorbitol-6-phosphate also inhibited G6P activation of SPS. Our results suggest that sucrose biosynthesis may be altered by the products of sorbitol biosynthesis in apple leaves.
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
