Chlorophyll b containing liposomes: Effect of thermal transitions on catalytic and spectral properties

Abstract

1. 1.Chlorophylls a and b were incorporated into saturated and unsaturated phosphatidylcholine liposomes. The red absorption bands of the two chlorophylls were at 671 nm and 651 nm, respectively, both in liposomes containing egg phosphatidylcholine and in liposomes containing saturated lecithins above their transition temperatures. 2. 2.In dipalmitoylphosphatidylcholine liposomes the absorption bands of chlorophyll b show a red shift on cooling below the transition temperature. Chlorophyll b broadens and depresses the transition temperature region of hydrated dipalmitoylphosphatidylcholine. 3. 3.Chlorophyll b containing liposomes catalyse the reduction of cytochrome c by trimethylhydroquinone in a light-sensitive reaction; the catalysis by egg lecithin liposomes has a rate about 60% that of Triton-dispersed chlorophyll and shows no sharp temperature effects, but the catalysis by dipalmitoyllecithin liposomes is only seen above their transition temperature. 4. 4.Chlorophyll b containing dimyristoyllecithin liposomes show a smaller spectral shift and a less marked increase in catalytic activity on passing through their transition temperature. 5. 5.Chlorophyll a containing saturated liposomes show smaller spectral and catalytic responses to temperature than do the chlorophyll b containing liposomes.