Resolution of two molecular forms of sucrose-phosphate synthase from maize,soybean and spinach leaves

Two forms of sucrose-phosphate synthase (EC 2.4.1.14) were resolved from leaves of three species, maize (Zea mays L. cv. Pioneer 3184), soybean (Glycine max (L.) Merr., cv. Ransom) and spinach (Spinacia oleracea L. cv. Resistoflay) by hydroxyapatite Ultrogel chromatography, using a 75-mM (designated peak 1) and 250-mM (peak 2) K-phosphate discontinuous-gradient elution. Rechromatography of the two forms showed that they were not readily interconvertible. The distribution of activity between the two forms differed among species and changed during purification of the enzyme. Recovery of peak-1 activity was specifically lowered when maize leaf extracts were prepared in the absence of magnesium, indicating that the two forms may differ in stability. In addition, the forms of the enzyme from maize differed in the extent of glucose-6-phosphate activation. These results provide evidence for the existence of multiple forms of sucrose-phosphate synthase in leaves of different species and that the forms differ in regulatory properties.Abbreviations Fru6P fructose 6-phosphate - Glc6P glucose 6-phosphate - HAU hydroxyapatite Ultrogel - Pi inorganic phosphate - SPS sucrose-phosphate synthase - UDP uridine 5-diphosphate - UDPG uridinediphosphate glucose Cooperative investigations of the United States Department of Agriculture, Agricultural Research Service, and the North Carolina Agricultural Research Service, Raleigh. Paper No. 10511 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh. Supported in part by USDA Competitive Research Grant No. 85-CRCR-1-1568