Sucrose biosynthesis in a prokaryotic organism: Presence of two sucrose-phosphate synthases in Anabaena with remarkable differences compared with the plant enzymes

A.C. PORCHIA; G.L. SALERNO

PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA

National Academy of Sciences, USA

Lugar: Washington, USA; Año: 1996 vol. 93 p. 13600 - 13604

0027-8424

<!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; mso-bidi-font-size:11.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman"; mso-ansi-language:EN-US;} p.MsoFooter, li.MsoFooter, div.MsoFooter {margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; tab-stops:center 212.6pt right 425.2pt; font-size:10.0pt; mso-bidi-font-size:11.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman"; mso-ansi-language:EN-US;} @page Section1 {size:595.3pt 841.9pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:35.4pt; mso-footer-margin:35.4pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> 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 (Km for SPS-I = 0.8 ± 0.1 mM; Km for SPS-II = 0.7 ± 0.1 mM) and UDP-Glc as substrates (Km for SPS-I = 1.3 ± 0.4 mM; Km 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 (Km for GDP-Glc =  1.2 ± 0.2 mM and Km for TDP-Glc = 4.0 ± 0.4 mM), and ADP-Glc is used by SPS-II (Km 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 SDSyPAGE, showed a monomeric composition. Cyanobacteria are, as far as the authors know, the most primitive  organisms