Isolation of a Photosystem II Associated 36 kDa Polypeptide and an Iron-Stress 34 kDa Polypeptide from Thylakoid Membranes of the Cyanobacterium Synechococcus PCC 6301 Grown under Mild Iron Deficiency

A 36 kDa polypeptide which previously was shown to be present in purified photosystem II complexes from Synechococcus PCC 6301 and which crossreacts with the antiserum raised against the soluble L-amino acid oxidase o f 50 kDa from Synechococcus PCC 6301 (A. E. Gau, G. Wälzlein, S. Gärtner, M. Kuhlmann, and E. K. Pistorius, Z. Naturforsch. 44c, 971, 1989), was isolated from thylakoid membranes o f the same cyanobacterium grown under mild iron deficiency. This peptide is present in about equal amounts in thylakoid membranes o f Syne­ chococcus PCC 6301 grown under regular or iron deficient conditions. The antiserum raised against this thylakoid membrane bound 36 kDa peptide crossreacts with the soluble L-amino acid oxidase o f 50 kDa. These results further support our conclusion that the thylakoid mem­ brane bound 36 kDa polypeptide is a modified form o f the soluble 50 kDa L-amino acid oxi­ dase. In addition, a 34 kDa polypeptide was isolated from iron stressed thylakoid membranes, and an antiserum was also raised against this protein. Immunoblot experiments with this an­ tiserum show that the 34 kDa peptide is present in elevated amounts in thylakoid membranes from Synechococcus cells grown under iron deficiency and that it is almost absent in thylakoid membranes from cells grown under regular conditions.