5 pages, figures, and tables statistics.Isolated D1 -D2-cytochrome b559 photosystem I1 reaction center preparations with pigment
stoichiometry higher than 4 chlorophylls per 2 pheophytins can be contaminated with CP47 proximal
antenna complex. Reaction centers prepared by a modification of the Nanba-Satoh procedure and
containing about 6 chlorophylls per 2 pheophytins showed immuno-cross-reactivity when probed with a
monoclonal antibody raised against the CP47 polypeptide. Furthermore, they could be fractionated
successfully by Superose- 12 sieve chromatography into two different populations. The first few fractions
off the column contained a more definitive 435 nm shoulder corresponding to increased chlorophyll content,
and showed strong immuno-cross-reactivity with the CP47 antibody. The peak fractions off the column
displayed a less prominent 435 nm shoulder, and did not cross-react with the antibody. Moreover, when
a 6-chlorophyll preparation was mixed with Sepharose beads coupled to CP47 antibody, the eluted material
corresponded to a preparation of about 4 chlorophylls per 2 pheophytins and did not show any crossreaction
with the antibody against CP47. The amount of CP47 protein in the 6-chlorophyll preparation
as quantitated using Coomassie Blue staining or from gel blots was sufficient to account for most of the
extra 2 chlorophylls. We conclude that D 1 -D2-cytochrome b559 preparations containing more than 4
chlorophylls per 2 pheophytins can be contaminated with small amounts of CP47-D1 -D2-Cyt b559
complex and that native photosystem I1 reaction centers contain 4 core chlorophylls per 2 pheophytins.Peer reviewe
