The primitive rhodophyte Cyanidioschyzon merolae contains a semiamylopectin-type, but not an amylose-type, alpha-glucan.

The storage glucans of Cyanidioschyzon merolae [clade L-1 (cyanidian algae), order Porphyridiales, subclass Bangiophycidae], which is considered to be one of the most primitive rhodophytes, were analyzed to understand the early evolution of the glucan structure in the Rhodophyta. Chain-length distribution analysis of the glucans of cyanidian algae demonstrated that while the glucans of Cyanidium caldarium and Galdieria sulphuraria are of the glycogen type, those of C. merolae are of the semiamylopectin type, as in other lineages of the Rhodophyta. Gel permeation chromatography, however, showed that the glucans of C. merolae do not include amylose, being different from those of other Bangiophycidae species. Identification by MALDI-TOF-MS and enzyme assaying of glucan granule-bound proteins indicated that phosphorylase, but not starch synthase, is included. Thus, C. merolae has an unusual glucan and bound-protein composition for the Bangiophycidae, appearing to be a member of the Florideophycidae. The finding that the alga does not contain amylose or the related enzyme, granule-bound starch synthase, is, however, consistent with previously reported results of molecular phylogenetic analysis of starch synthases. Our results support an evolutionary scenario defined by the loss of starch and reversion to glycogen synthesis during the evolution of cyanidian algae, and suggest the possibility that a C. merolae-like primitive rhodophyte might have evolved into the Florideophycidae.

The heterotrophic dinoflagellate Crypthecodinium cohnii defines a model genetic system to investigate cytoplasmic starch synthesis.

The nature of the cytoplasmic pathway of starch biosynthesis was investigated in the model heterotrophic dinoflagellate Crypthecodinium cohnii. The storage polysaccharide granules were shown to be composed of both amylose and amylopectin fractions with a chain length distribution and crystalline organization very similar to those of green algae and land plant starch. Preliminary characterization of the starch pathway demonstrated that C. cohnii contains multiple forms of soluble starch synthases and one major 110-kDa granule-bound starch synthase. All purified enzymes displayed a marked substrate preference for UDP-glucose. At variance with most other microorganisms, the accumulation of starch in the dinoflagellate occurs during early and mid-log phase, with little or no synthesis witnessed when approaching stationary phase. In order to establish a genetic system allowing the study of cytoplasmic starch metabolism in eukaryotes, we describe the isolation of marker mutations and the successful selection of random recombinant populations after homothallic crosses.

The identification of starch phosphorylase in the developing mungbean (Vigna radiata L.).

Starch phosphorylase (SP) in immature mungbean (Vigna radiata L. cv KPS1) seed soluble extract was detected by in situ activity staining and identified by MALDI-TOF mass analysis. After in situ SP assay on native-PAGE, a major starch-enzyme complex was located on the gel zymogram in a dose-dependent manner. This complex depicted two major SP-activity related proteins, 105 kDa and 55 kDa, by SDS-PAGE. The mass and predicted sequence of the tryptic fragments of the isolated 105 kDa protein, analyzed by MALDI-TOF spectroscopy and bioinformatic analysis, confirmed it to be mungbean SP as a result of high similarity to the L-SP of known plant. Polyclonal antibodies raised from the 55 kDa recognized both the 105 kDa and the 55 kDa proteins on the Western blot and neutralized partial SP activity, indicating that the two proteins were immunologically related. The 55 kDa protein possess high similarity to the N-terminal half of the 105 kDa SP was further confirmed. The SP activity and the activity stained protein density in mungbean soluble extract decreased as the seed size increased during early seed growth. These data indicate that mungbean 105 kDa SP and SP activity-related 55 kDa were identified in the developing mungbean.