Rubisco large subunit

Chloroplasts come in various sizes and shapes, but all contain a small number of DNA molecules ranging in size from 120-160 kb. Complete sequences are known for DNA from chloroplasts of a liverwort (121,025 bp),246 tobacco (155,844 bp),247 maize (Zea mays),248 and other plants. The 140,387 bp DNA from maize chloroplasts is a circular molecule containing the genes for 23S, 16S, 5S, and 4.5S RNA, for 30 species of tRNA, and for 70 different proteins. Among them are subunits of RNA polymerase, NADH dehydrogenase, subunits of both PSI and PSII, rubisco (large subunit), cytochromes b and/, six subunits of ATP... 

V. Irihimovitch and M. Shapira. 2000. Glutathione redox potential modulated by reactive oxygen species regulates translation of rubisco large subunit in the chloroplast J. Biol. Chem. 275 16289-16295. (PubMed)... 

A27. Shikanai, T., C.H. Foyer, H. Dulieu, M.A.J. Parry, and A. Yokota A point mutation in the gene encoding the Rubisco large subunit interferes with holoenzyme assembly Plant Mol. Bio. 31 (1996) 399 03. 

TABLE 1. The effect of BP on the solubility of Rubisco large subunit. Rubisco was dissociated into subunits in the absence (control) or presence of BP (experiment) (see Materials and methods). The total amounts and the molar ratio of Rubisco subunits (L/S) are indicated. The theoretical value for the molar ratio of subunits in holoprotein is 1. 

Figure 1 Amino acid sequence at the C-terminus of Rubisco large subunit from R.rubrum (residue to The a-helices are...

PW512 641 bp coding for wheat Rubisco SSU (Smith, S. M., Bedbrook. J. and Speirs, J., 1983). pZ]nc37 2500bp coding for maize Rubisco large subunit (LSU) (Bedbrook et al., 1979). 

T thylakoid S stroma IM inner membrane OM outer membrane c untreated control (30 g) o organic phase a aqueous phase LS RubisCO large subunit SS RubisCO small subunit 100 g of each fraction were submitted to TX-114 phase partition (one third of the stroma aqueous phase was loaded)... 

Case 3 Stroma, Inner and Outer envelope membranes 54 kPa After proteosynthesis and TX-114 phase partition, a radioactive 54 kDa band was found in the organic phases of the stroma, the inner and outer envelope membranes at the level of the RubisCO large subunit (LS) (fig.1). The RubisCO is a known contaminant of the envelope membrane and has been, so far, impossible to eliminate. As the TX-114 partitioning was shown to be reliable, we tried to find out whether this 54 kDa Coomassie band was the LS or not. First, an antibody against the RubisCO (kindly provided by Dr. A. Radunz) was tested on the three treated fractions as well as on their respective controls (fig.2). 

Fig. 3.7 Transgenic rapeseeds were sprouted in an airlift tank with (lane 1) and without (lane 2) of streptomycin at 100 mg L-1. Total proteins were extracted, separated by SDS-PAGE and stained with Coomassie blue. The synthesis of Rubisco large and small subunits was inhibited as clearly shown in lane 2.

As a response to cold treatment there is a modification both in the level and in the activity of many important enzymes. In rice the mRNA coding for the Rubisco small subunit decreases drastically at low temperature, as do the levels of both the small and large Rubisco subunits (Hahn Walbot, 1989). In rye Huner Macdowall (1979) also observed structural and functional changes in Rubisco during growth at low temperature. 

Over two dozen crystal structures of Rubisco have been resolved. For most cases, the enzyme is assembled into a large complex with 4 large subunits (L 475 residues) and 4 small subunits (S 123 residues) assembled as a dimer (L4S4)2 of ca 550 kDa (Figure 16). 

Figure 20.3. Structure of Rubisco. The enzyme ribulose 1,5-bisphosphate carboxylase/oxygenase (rubisco) comprises eight large subunits (one shown in red and the others in yellow) and eight small subunits (one shown in blue and the others in white). The active sites he in the large subunits.

The term "molecular chaperone" is not novel and was first introduced (7) to describe the transient association of nucleoplasmin with the histones during the formation of nucleosomes. Subsequently, a similar transient association was found in the chloroplast of higher plants between nascent Large subunits (LSU) of die enzyme Ribulose bisphosphate carboxylase (Rubisco) and a SdOkDa protein complex composed of 12-14 60kDa subunits (2). The nascent chloroplast-synthesized LSU was found to bind this complex in a non-covalent manner and in sub-stoichiometric amounts. 

The genes that code for ribulose- 1,5-bisphosphate carboxylase (rubisco) are found within the chloroplast (the L subunit) and the nucleus (the S subunit). The activation of these genes is mediated by an increase in light intensity (illumination). Phytochrome also appears to play a role in this activating process. Once the S subunit is transported from the cytoplasm into the chloroplast, both subunits assemble to form the L8S8 holoenzyme. A protein called the large subunit-binding protein appears to assist in the assembly of the holoenzyme. When illumination is low, the synthesis of both subunits is rapidly depressed. 

The reaction that actually fixes CO2 into carbohydrates is catalyzed by ribulose 1,5-bisphosphate carboxylase (often called rubisco), which is located in the stromal space of the chloroplast. This enzyme adds CO2 to the five-carbon sugar ribulose 1,5-bisphosphate to form two molecules of 3-phosphoglycerate (Figure 8-41). Rubisco is a large enzyme ( 500 kDa) composed of eight identical large subunits and eight identical small subunits. One subunit is encoded in chloroplast DNA the other, in nuclear DNA. Because the catalytic rate of rubisco is quite slow, many copies of the enzyme are needed to fix sufficient CO2. Indeed, this enzyme makes up almost 50 percent of the chloroplast protein and is believed to be the most abundant protein on earth. 

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