PROPERTIES OF PRIMER-DEPENDENT STARCH SYNTHESIS CATALYZED BY STARCH SYNTHASE FROM POTATO-TUBERS

A starch synthase was partially purified from soluble extracts of potato tubers by successive chromatographic separation on maltotriose-bovine serum albumin conjugated to Sepharose, DEAE-Toyopearl 650-S and Sepharose CL-6B columns. The enzyme activity was completely dependent on added primer. Enzyme activity increased with increasing concentrations of sodium citrate, but sodium citrate was not absolutely necessary for the activity. Rabbit liver glycogen was the best primer for the enzyme, whereas malto-oligosaccharides were not effective. The enzyme elongated only α-1,4-linked chain by transferring glucose from ADPGlc into the primer. Thus, this particular starch synthase is different from already known enzymes of this type in several respects, notably its primer requirement, its specificity toward primers, and the stimulation of the primed reaction with sodium citrate. © 1990.