Plant-type Photosynthesis Research Articles

A novel nucleic acid-binding protein in the cyanobacterium Synechococcus sp. PCC6301: a soluble 33-kDa polypeptide with high sequence similarity to ribosomal protein S1

Cyanobacteria are prokaryotes that carry out plant-type photosynthesis and contain several eukaryotic-type RNA-binding proteins. Using a single-stranded DNA column, a 33-kDa protein was isolated and characterized from Synechococcus sp. PCC6301. This protein of 293 amino acids is similar in overall structure to the ribosomal protein S1 found in the same species, and contains three repeated units that are highly similar to the S1 motif originally found in the ribosomal protein S1 of Escherichia coli. However, the 33-kDa protein was found not to be associated with ribosomes and its nucleic acid binding specificity is distinct from that of the ribosomal protein S1. As this protein has high affinity for both single- and double-stranded DNA, as well as for poly(G) and poly(A), we tentatively named it nucleic acid-binding protein 1 (Nbp1).

Catalase-Peroxidases in Cyanobacteria – Similarities and Differences to Ascorbate Peroxidases

Cyanobacteria (blue-green algae) are oxygenic phototrophic bacteria carrying out plant-type photosynthesis. The only hydrogen peroxide scavenging enzymes in at least two unicellular species have been demonstrated to be bifunctional cytosolic catalase-peroxidases (CatPXs) having considerable homology at the active site with plant ascorbate peroxidases (APXs). In this paper we examined optical and kinetic properties of CatPXs from the cyanobacteria Anacystis nidulans and Synechocystis PCC 6803 and discuss similarities and differences to plant APXs. Both CatPXs and APX showed similar spectra of the ferric enzyme, the redox intermediate Compound I and the cyanide complex, whereas the spectrum of CatPX Compound II had characteristics reminiscent of the spectrum of the native enzyme. Both steady-state and multi-mixing transient-state kinetic studies were performed in order to characterize the kinetic behaviour of CatPXs. Bimolecular rate constants of both formation and reduction of a CatPX Compound I are presented. Because of its intrinsic high catalase activity (which cannot be found in APXs), the rate constants for Compound I formation were measured with peroxoacetic acid and are shown to be 5.9 x 10(4) M(-1) s(-1) for CatPX from A. nidulans and 8.7 x 10(3) M(-1) s(-1) for the Synechocystis enzyme. Compared with o-dianisidine (2.7-6.7 x 10(6) M(-1) s(-1)) and pyrogallol (8.6 x 10(4)-1.6 x 10(5) M(-1) s(-1)), the rate constant for Compound I reduction by ascorbate was extremely low (5.4 x 10(3) M(-1) s(-1) at pH 7.0 and 15 degrees C), in marked contrast to the behaviour of APXs.

Composition and development of the bacterial photosynthetic apparatus.

The order of the Rhodospirillales, commonly known as the photosynthetic or more adequately as the phototrophic bacteria, comprises prokaryotes that are able to cover their energy requirements by coupling to light-dependent electron transport processes. In contrast to the plant-type photosynthesis not only of plants but also of cyanobacteria, the photosynthesis of phototrophic bacteria does not evolve oxygen and is dependent on anaerobiosis or, at least, largely reduced oxygen partial pressures. Apart from these physiological characteristics, the phototrophic bacteria comprise organisms of rather different properties (see Table I for the classification of phototrophic bacteria referred to in this chapter). Based on the distribution of different bacteriochlorophyll derivatives contained in the photosynthetic apparatus, two suborders can be distinguished (Truper and Pfennig, 1978). The first suborder of the Rhodospirillineae, i.e., the purple bacteria, comprises organisms that exhibit either bacteriochlorophyll a or b. This suborder contains two families, the Rhodospirillaceae (formerly Athiorhodaceae) and the Chromatiaceae (formerly Thiorhodaceae), which differ from each other by their inability and ability, respectively, to grow on sulfide (exceptions are known). The second suborder, the Chlorobiineae, comprises all of the phototrophic bacteria that produce bacteriochlorophyll c, d, or e, in addition to minor quantities of bacteriochlorophyll a.