title: 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.
abstract: Cryptonemia crenulata biosynthesizes a family of dl-hybrid galactans that are based on the classical 3-linked beta-d-galactopyranosyl-->4-linked alpha-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 beta-D-xylose and/or beta-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 (alpha-galactose 6-sulfate (major) and alpha-galactose 2,6-sulfate, minor). Kinetic studies show a rate constant, for the diad G2S-D(L) 6-S, of 1.7 x 10(4)s(-1) indicating a reaction faster than in lambda-carrageenans but slower than in porphyrans.
authors.affiliation: Departamento de Bioquímica e Biologia, Molecular, Universidade Federal do Paraná, PO Box 19046, CEP: 81531-990 Curitiba-Paraná, Brazil.
authors.forename: Rosiane G M
authors.initials: RG
authors.lastname: Zibetti
authors.forename: Miguel D
authors.initials: MD
authors.lastname: Noseda
authors.forename: Alberto S
authors.initials: AS
authors.lastname: Cerezo
authors.forename: Maria E R
authors.initials: ME
authors.lastname: Duarte
mesh_terms: D002852:Chromatography, Ion Exchange; D003500:Cyclization; D005685:Galactans / Q000737:chemistry* / Q000302:isolation & purification*; D006878:Hydroxides / Q000737:chemistry*; D007700:Kinetics; D008745:Methylation; D019906:Nuclear Magnetic Resonance, Biomolecular; D000461:Rhodophyta / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D005685:Galactans; D006878:Hydroxides