Concentration and Function of Membrane-Bound Cytochromes in Cyanobacterial Heterocysts

• Published in: Plant physiology (Bethesda) 1984-10, Vol.76 (2), p.456-460
• Main Authors: Jeffrey P. Houchins, Hind, Geoffrey
• Format: Article
• Language: English
• Subjects: Anabaena; Analytical, structural and metabolic biochemistry; Biological and medical sciences; Cell membranes; Chloroplasts; Cyanobacteria; Cytochromes; Electron transfer; Electron transport chain; Fundamental and applied biological sciences. Psychology; Hemoproteins; heterocysts; Metalloproteins; Oxidases; Plants; Proteins; Quinones; Somatic cells
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.76.2.456

Membranes isolated from heterocysts and vegetative cells of Anabaena 7120 were assayed for content of cytochrome f, cytochrome b-563, cytochrome $b-559_{\text{HP}}$, cytochrome $b-559_{\text{LP}}$, and cytochrome aa3 by use of reduced-minus-oxidized difference spectra. The level of cytochrome aa3 in heterocyst membranes was 4 to 100 times higher than that in vegetative cells of Anabaena 7120 or other species of cyanobacteria. Heterocyst membranes lack cytochrome $b-559_{\text{HP}}$ but contain cytochrome $b-559_{\text{LP}}$ ($E_{m7.5}$ = +77 millivolts, n = 1) at approximately the same concentration as cytochrome f. The role of cytochrome $b-559_{\text{LP}}$ in the hydrogenase-dependent electron transfer pathway was investigated with the inhibitor 2-(n-heptyl)-4-hydroxyquinoline N-oxide which blocks electron flow from hydrogenase to acceptors reacting with the plastoquinone pool. Addition of inhibitor elicited no change in the reduction level of cytochrome $b-559_{\text{LP}}$ indicating that this cytochrome is not directly involved in this pathway.