Gr. Wolfe et al., ISOLATION AND CHARACTERIZATION OF PHOTOSYSTEM-I AND PHOTOSYSTEM-II FROM THE RED ALGA PORPHYRIDIUM-CRUENTUM, Biochimica et biophysica acta. Bioenergetics, 1188(3), 1994, pp. 357-366
Photosystem I and Photosystem II complexes were isolated from the red
alga Porphyridium cruentum (P. purpureum) following solubilization of
thylakoid membranes with dodecyl-B-D-maltoside. More than 90% of the t
otal chlorophyll was recovered in two green bands on a sucrose gradien
t. PS I and PS II complexes, present in the lower green band, were sep
arated by anion exchange chromatography. The purified PS II complex, w
ith an absorption maximum at 674 nm and a fluorescence emission maximu
m at 699 nm (77 K), contained the reaction center polypeptide D2 and t
he core antenna proteins CP43 and CP47 as shown by immunoblot analysis
. Two bands (<14 kDa), presumably the cyt b-559 subunits were also obs
erved after silver-staining SDS-PAGE gels. The photoactivity rate of 5
8 mu mol DCPIP/mg Chi per h with DPC for PS II core complexes, and 112
mu mol DCPIP/mg Chi per h for thylakoids (minus phycobilisomes), was
sensitive to DCMU inhibition. The purified PS I holocomplex had approx
130 chlorophyll per P700, an absorption maximum at 680 nm and a fluor
escence emission maximum at 730 nm (at 77 K). Prominent silver-stained
bands in SDS-PAGE gels at 62 and 57 kDa polypeptides were immunologic
ally identified as the P700 apoproteins. Polypeptides of 23.5, 23, 22,
20, 19.5, 18, 16.5, 15.5, and 11 kDa and at least three low molecular
mass polypeptides (< II kDa) were also observed. Of particular intere
st are the 18-23.5 kDa polypeptides in the PS I complex, since such po
lypeptides were previously unknown in phycobilisome-containing organis
ms. In fact, we have found that the PS I complex of P. cruentum is str
ucturally similar to that of higher plants, especially since polypepti
des of 18-23.5 kDa were shown to be immunologically related to LHC I o
f higher plants (Wolfe, G. et al. (1994) Nature 367, 566-568). These r
esults clearly suggest that the thylakoid structure of this red alga i
s more complex than in cyanobacteria, which like rhodophytes, also hav
e phycobilisomes as major antenna complexes.