ULTRASTRUCTURAL EVIDENCE FOR INTRAMOLECULAR DOUBLE STRANDING IN IOTA-CARRAGEENAN

Kinetic studies of primary processes of conformational ordering in gel -forming biopolymers have suggested that a change in mechanism from in termolecular to intramolecular multistrand formation occurs on lowerin g the concentration of biopolymer. We report here ultrastructural obse rvations consistent with intramolecular double stranding in a carbohyd rate polymer, iota-carrageenan, by arresting this process of primary c onformational ordering by an ultra-rapid freeze fixation technique. Hi gh-resolution transmission electron microscopy (TEM) revealed isolated iota-carrageenan chains showing a range of morphologies (linear, circ ular, and hairpin) consistent with intramolecular stranding. Control e xperiments in which iota-carrageenan was frozen in the disordered form revealed longer and thinner strands.