Purification and Further Characterization of Pyrenoid Proteins and Ribulose-1,5-bisphosphate Carboxylase-Oxygenase from the Green Alga <italic>Bryopsis maxima</italic>

Abstract

Pyrenoid proteins and ribulose-1,5-bisphosphate carboxylase-oxygenase (RuBisCO) in the green alga Bryopsis maxima were purified to high degrees and their peptide compositions were studied by SDS-polyacrylamide gel electrophoresis. RuBisCO had a large subunit of 50 kDa and a small one of 16 kDa. The apparent molecular weight of the purified RuBisCO was estimated as 460 kDa by gel filtration. Pyrenoid proteins had two major polypeptides: 52 kDa and 17 kDa. The peptide map of the 52 kDa pyrenoid polypeptide coincided well with that of the large subunit of RuBisCO, strongly suggesting that the major component of the pyrenoid of this alga was RuBisCO. We attempted to survey the distribution of RuBisCO in the chloroplasts. The results suggested that much of the RuBisCO of Bryopsis maxima was localized in the pyrenoid. The pyrenoid also contained more than 10 minor polypeptides not found in the RuBisCO fraction. The minor polypeptides comprised about 15% of the total pyrenoid protein and differed from the polypeptides of the thylakoid membranes and from those found in the starch grains surrounding the pyrenoid.