J. Biol. Chem., Vol. 261, Issue 18, 8134-8139, Jun, 1986
Identification and analysis of the maize P700 chlorophyll a apoproteins PSI-A1 and PSI-A2 by high pressure liquid chromatography analysis and partial sequence determination
LE Fish and L Bogorad
We recently described a pair of partially homologous maize chloroplast
genes, one of which was shown to code for an apoprotein of the P700
chlorophyll a complex of photosystem I (Fish, L.E., Kuck, U., and Bogorad,
L. (1985) J. Biol. Chem. 260, 1413-1421). Two chlorophyll-free apoprotein
bands from maize chlorophyll-protein complex I (CPI) can be resolved on
lithium dodecyl sulfate (LDS)-urea polyacrylamide gels. Proteins in both
bands react with antibodies prepared against CPI, but antibodies prepared
against two synthetic peptides corresponding to predicted sequences of
PSI-A1 react only with the upper band. The presence of products of the two
genes, ps1A1 and ps1A2, in CPI was verified by analysis of cyanogen bromide
(CNBr) fragments of the lower apoprotein band obtained from LDS-urea
polyacrylamide gels by reverse- phase high pressure liquid chromatography.
Amino-terminal sequencing of five CNBr fragments indicates that the lower
band contains a product of the ps1A2 gene. The possibility of extensive
processing was investigated because the apparent molecular masses of the
maize CPI proteins are about 58-70 kDa on LDS-polyacrylamide gels rather
than the predicted sizes of about 83 kDa. Antibodies against a synthetic
peptide corresponding to a predicted sequence in PSI-A1 were used to
determine that the amino-terminal end of PSI-A1 is intact beyond about
position 52. The amino-terminal CNBr fragment of PSI-A2 was identified by
sequencing, indicating that the amino-terminal end of PSI-A2 is not
processed. The carboxyl-terminal CNBr fragment of PSI-A2 was also
identified by sequencing. These results indicate that the PSI-A1 and PSI-A2
polypeptides are not extensively processed, although some processing at the
carboxyl-terminal end has not been ruled out.