The system of galactans from Cryptonemia crenulata (Halymeniaceae, Halymeniales) and the structure of two major fractions. Kinetic studies on the alkaline cyclization of the unusual diad G2S→D(L)6S
Cryptonemia crenulata biosynthesizes a family of dl-hybrid galactans that are based on the classical 3-linked β-d-galactopyranosyl→4-linked α-galactopyranosyl alternating sequence (A-units→B-units). The dispersion of structures in these galactans is based on four factors, namely: (a) the amount and...
Guardado en:
| Autores principales: | , |
|---|---|
| Publicado: |
2005
|
| Materias: | |
| Acceso en línea: | https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_00086215_v340_n4_p711_Zibetti http://hdl.handle.net/20.500.12110/paper_00086215_v340_n4_p711_Zibetti |
| Aporte de: |
| Sumario: | Cryptonemia crenulata biosynthesizes a family of dl-hybrid galactans that are based on the classical 3-linked β-d-galactopyranosyl→4-linked α-galactopyranosyl alternating sequence (A-units→B-units). The dispersion of structures in these galactans is based on four factors, namely: (a) the amount and position of substituent groups as sulfate (major), pyruvic acid ketals, methoxyl and side substituents of β-d-xylose and/or β-d-galactose; (b) the ratio galactose/3,6-anhydrogalactose in the B-units; (c) the ratio d-/l-galactoses and 3,6-anhydrogalactoses also in the B-units and (d) the sequence of the diads in the linear backbone. Alkali treatment carried out on the major fraction produced a nearly quantitative formation of 3,6-anhydrogalactose units from precursor units (α-galactose 6-sulfate (major) and α-galactose 2,6-sulfate, minor). Kinetic studies show a rate constant, for the diad G2S-D(L) 6-S, of 1.7 × 104 s -1 indicating a reaction faster than in λ-carrageenans but slower than in porphyrans. © 2005 Elsevier Ltd. All rights reserved. |
|---|