Abstract
Electron spin resonance linewidth measurements have been made on intact cell walls exchanged with various combinations of Mn 2+ and Ca 2+. These experiments were performed to find the Mn 2+ nearest-neighbor distance and thereby determine whether carboxylate-Mn 2+ complexes potentiate ion association at adjacent sites on cell wall polyuronides. Our results show that as the fraction of available binding sites occupied by Mn 2+ increased from 2% to 27%, the nearest-neighbor distance parameter decreased only from 14 to 11 Å. These distances are close to polyuronide interanionic spacings. The small change in the distance parameter with concentration is evidence for sequential rather than random binding. Competitive ion-exchange with Ca 2+ was found to reduce the Mn 2+ spin-spin line broadening at similar total bound Mn 2+ concentrations. This is expected only if Ca 2+ competes at adjacent sites. The data presented offer strong support for the hypothesis that carboxylate groups near already occupied sites have a greater affinity for divalent cations than other sites along the polyuronide main chain.
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Schedule a callMore From: Biochimica et Biophysica Acta (BBA) - Molecular Cell Research
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