An immunological and electrophoretic comparison of the thylakoids from vegetative cells and heterocysts ofAnabaena cylindrica

Abstract

An antiserum prepared to Triton-solubilized thylakoid membranes isolated from the vegetative cells of Anabaena cylindrica cross-reacts in the Ouchterlony double immunodiffusion test to produce four precipitin bands with the homologous antigens. Solubilized heterocyst thylakoids only react to produce two bands with the above antiserum. The antiserum also produced a heavier total immunoprecipitation with vegetative cell thylakoids than with similar amounts of heterocyst thylakoid proteins. The immunological evidence that the vegetative cell thylakoids contain proteins which are either not present in heterocysts, or become modified during heterocyst differentiation, is supported by differences in the polypeptide compositions of the membranes from the two cell types. Sodium dodecyl sulphate (SDS)—solubilization followed by SDS acrylamide gel electrophoresis revealed 13 bands in the vegetative thylakoid samples but only eight with the heterocyst material. No polypeptide molecular weight species were present in the heterocyst samples which were not also present in the vegetative cell membranes, suggesting that de novo thylakoid synthesis during heterocyst differentiation, previously proposed from electron microscopy studies, must only involve the formation of molecular weight classes of polypeptides already present in the vegetative cells.