Regulation of betacyanin efflux from beet root by poly-L-lysine, ca-ion and other substances

Abstract

Poly-l-lysine, poly-alpha, gamma-diaminobutyric acid and basic proteins cause efflux of betacyanin from beet root tissues to varying degrees. Membrane activities fall in the order: polylysine > poly-alpha, gamma-diaminobutyric acid > polyarginine (protamine), suggesting the importance of steric factors in side-chain to backbone relations. It was also observed that homopolymer activity > heteropolymer activity, using ribonuclease and lysozyme as examples of the latter. Among polylysines, there appears to be an optimal chain length at a molecular weight equal to 50,000. Lowered activity of larger polymers is interpreted in terms of a diffusion barrier, the cell wall.Polylysine and Ca(++) exhibit competitive kinetics, and Ca(++) otherwise is far more active than other cations. It is assumed that polylysine displaces Ca(++) from anionic centers on the membrane, but cannot confer equivalent dimensional stability, rendering the membrane leaky. The possible role of cationic shielding in ionic stabilization of the membrane was also considered. The order of divalent ion activity against polylysine was Ca(++) > Sr(++) > Mg(++), suggesting again a specific size-fit relationship.