Acetylation and methylation of homogalacturonans - 2: effect on ion-binding properties and conformations

Acetylated citrus pectin and pectate (DAc of 213 and 150, respectively) wer e prepared; they were soluble in ethanol (up to 90%) or acetone and did not precipitate or form gels in the presence of calcium, zinc or lead. Binding isotherms indicated a loss of the cooperative behaviour with acetylation, particularly for zinc and calcium. Partially methylated and acetylated homo galacturonans showed different effects of methyl and acetyl substitution on binding of calcium, zinc and lead. Calcium and lead salts of partially met hylated homogalacturonans adopted different conformations in the dry state, as indicated by their C-13 CP-MAS NMR spectra: whereas calcium homogalactu ronans could adopt (partially) a 2(1) conformation which was lost at higher degrees of methylation, lead salts kept the same, 3(1), conformation for a ll degrees of methylation. C-13 CP-MAS NMR spectra of partially acetylated homogalacturonans showed the presence of a wide range of conformations with marked differences between the ions. (C) 1999 Elsevier Science Ltd. All ri ghts reserved.