Sucrose biosynthesis in a prokaryotic organism: Presence of two sucrose-phosphate synthases in Anabaena with remarkable differences compared with the plant enzymes.
Biosynthesis of sucrose-6-P catalyzed by sucrose-phosphate synthase (SPS), and the presence of sucrose-phosphate phosphatase (SPP) leading to the formation of sucrose, have both been ascertained in a prokaryotic organism: Anabaena 7119, a filamentous heterocystic cyanobacterium. Two SPS activities (SPS-I and SPS-II) were isolated by ion-exchange chromatography and partially purified. Four remarkable differences between SPSs from Anabaena and those from higher plants were shown: substrate specificity, effect of divalent cations, native molecular mass, and oligomeric composition. Both SPS-I and SPS-II accept Fru-6-P (K(m) for SPS-I = 0.8 +/- 0.1 mM; K(m) for SPS-II = 0.7 +/- 0.1 mM) and UDP-Glc as substrates (K(m) for SPS-I = 1.3 +/- 0.4 mM; K(m) for SPS-II = 4.6 +/- 0.4 mM), but unlike higher plant enzymes, they are not specific for UDP-Glc. GDP-Glc and TDP-Glc are also SPS-I substrates (K(m) for GDP-Glc = 1.2 +/- 0.2 mM and K(m) for TDP-Glc = 4.0 +/- 0.4 mM), and ADP-Glc is used by SPS-II (K(m) for ADP-Glc = 5.7 +/- 0.7 mM). SPS-I has an absolute dependence toward divalent metal ions (Mg2+ or Mn2+) for catalytic activity, not found in plants. A strikingly smaller native molecular mass (between 45 and 47 kDa) was determined by gel filtration for both SPSs, which, when submitted to SDS/PAGE, showed a monomeric composition. Cyanobacteria are, as far as the authors know, the most primitive organisms that are able to biosynthesize sucrose as higher plants do.
Porchia
A C
AC
Centro de Investigaciones Biológicas, Fundación para Investigaciones Biológicas Aplicadas, ProBiop (Conlcet), Mar del Plata, Argentina.
Salerno
G L
GL
D017033:Anabaena / Q000201:enzymology*; D002413:Cations, Divalent / Q000494:pharmacology; D002850:Chromatography, Gel; D002852:Chromatography, Ion Exchange; D005964:Glucosyltransferases / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D007527:Isoenzymes / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D007700:Kinetics; D046911:Macromolecular Substances; D008970:Molecular Weight; D010944:Plants / Q000201:enzymology*; D013379:Substrate Specificity; D013395:Sucrose / Q000378:metabolism
D002413:Cations, Divalent; D007527:Isoenzymes; D046911:Macromolecular Substances; D013395:Sucrose; D005964:Glucosyltransferases; C022698:sucrose-phosphate synthase