Purification and characterization of the photosystem I complex from the filamentous cyanobacterium Anabaena variabilis ATCC 29413.

A photoactive photosystem I complex has been purified from the filamentous, nitrogen-fixing cyanobacterium Anabaena variabilis ATCC 29413. Cells were broken using glass beads, and the membrane fraction was solubilized with beta-dodecyl maltoside followed by two rounds of fast protein liquid chromatography on anion exchange columns. The polypeptide composition of the isolated complex was determined by sodium dodecyl sulfate-urea-polyacrylamide gel electrophoresis and N-terminal amino acid sequencing of the fractionated proteins. The purified complex consists of at least 11 proteins, identified as the PsaA, PsaB, PsaC, PsaD, PsaE, PsaF, PsaI, PsaJ, PsaK, PsaL, and PsaN proteins. The spectrum of the flash-induced absorbance change measured between 670 and 830 nm shows that the purified complex contains 99 +/- 11 chlorophyll a molecules per P700, the primary donor in photosystem I. The kinetics of the rereduction of oxidized P700 following an actinic flash indicate that forward electron transfer from P700 to the FA/FB iron-sulfur center acceptors is functional in the isolated complex.