Ribulose 1.5-bisphosphate

Figure 4.8 The active site in all a/p barrels is in a pocket formed by the loop regions that connect the carboxy ends of the p strands with the adjacent a helices, as shown schematically in (a), where only two such loops are shown, (b) A view from the top of the barrel of the active site of the enzyme RuBisCo (ribulose bisphosphate carboxylase), which is involved in CO2 fixation in plants. A substrate analog (red) binds across the barrel with the two phosphate groups, PI and P2, on opposite sides of the pocket. A number of charged side chains (blue) from different loops as welt as a Mg ion (yellow) form the substrate-binding site and provide catalytic groups. The structure of this 500 kD enzyme was determined to 2.4 A resolution in the laboratory of Carl Branden, in Uppsala, Sweden. (Adapted from an original drawing provided by Bo Furugren.)...

As indicated, ribulose bisphosphate carboxylase/oxygenase catalyzes an alternative reaction in which Og replaces COg as the substrate added to RuBP (Figure 22.29a). The ribulose-l,5-bisphosphate oxygenase rezLCtion diminishes plant... 

RIBULOSE BISPHOSPHATE CARBOXYLASE LARGE CHAIN (EC 4.1.1.39). Anthoceros formosae. 

The virtual SWISS-PROT entries have a far-reaching effect on TrEMBL. For example, the virtual entry for the Rubisco (ribulose-bisphosphate carboxylase) large chain affects 3300 TrEMBL entries. Therefore a system has been developed to decompose these virtual entries into rules that are stored in a relational database with proper version control features. 

Bromo-l,4-dihydroxybutan-2-one 1,4-bisphosphate (31) has been prepared from the protected bromohydrin of cw-but-2-ene-l,4-diol.95 Nucleophiles rapidly displace bromide ion from (31), and the latter has been used as an affinity label for ribulose-bisphosphate carboxylase. In this case two sites are labelled in each enzyme molecule, the two molecules of (31) being linked to the enzyme by two different lysine residues.96... 

CAM (Crassulacean Acid Metabolism) photosynthetic pathway A variant of the C4 pathway phosphoenolpyruvate fixes C02 in C4 compounds at night, and then, the fixed C02 is transferred to the ribulose bisphosphate of the Calvin cycle within the same cell during the day. Characteristic of most succulent plants, such as cacti. 

In this reaction, one molecule of ribulose-1,5-bisphosphate (metabolite 1) and one molecule of CO2 (metabolite 2) give rise to two molecules of 3-phosphoglycerate (metabolite 3). The enzyme responsible has the EC number 4.1.1.39. The annotated enzyme list shows that this refers to ribulose bisphosphate carboxylase ( rubisco for short). Rubisco belongs to enzyme class 4 (the lyases) and, within that group, to subclass 4.1 (the car-boxy-lyases). It contains copper as a cofactor ([Cu]). 

Why is ribulose bisphosphate carboxylase (RUBISCO) a poor target for a herbicide ... 

The enzyme responsible for the fixation of CO2, ribulose bisphosphate carboxylase/oxygenase (RUBISCO), also catalyses the oxygenation of ribulose bisphosphate to form one molecule of phosphoglycerate and one molecule of phosphoglycolate. Under normal C02 and 02 concentrations six ribulose bisphosphate molecules react with oxygen for every 15 that react with carbon dioxide. 

Andersson, I., Knight, S., Schneider, G., Lindqvist, Y, Lundqvist, T., Briinden, C.-I., Lorimer, G.H. (1989) Crystal structure of the active site of ribulose-bisphosphate carboxylase. Nature 337, 229-234. 

C. Formation of carbamino groups In hemoglobin In ribulose bisphosphate carboxylase Eq. 7-23 Chapters 13,23... 

Phosphate and bicarbonate ions are important substrates for many enzymatic processes and as such have regulatory functions. Bicarbonate controls the key enzyme of photosynthesis, ribulose bisphosphate carboxylase, by carbamate formation (Fig. 13-12). Chloride ions activate amylases and may affect the action of "G proteins" that mediate hormone actions. Other observed effects of ions are too numerous to mention. 

A P-oxo acid, with proper catalysis, is susceptible to hydrolysis by attack of water on the carbonyl group. An example is the reaction catalyzed by oxaloacetate acetylhydrolase which has been isolated from Aspergillus niger (Eq. 13-34). A related cleavage is catalyzed by ribulose bisphosphate carboxylase (see Eq. 13-48). 

Ribothymidylic acid residue 813 Ribozyme(s) 649 - 652, 239 artificial 652 hairpin 649,651s hammerhead 649, 651 leadzyme, 651s Ribulose 164s Ribulose bisphosphate 707s Ribulose bisphosphate carboxylase (Rubisco)... 

An analogous use of ATP is found in photosynthetic reduction of carbon dioxide in which ATP phos-phorylates ribulose 5-P to ribulose bisphosphate and the phosphate groups are removed later by phosphatase action on fructose bisphosphate and sedoheptulose bisphosphate (Section J,2). Phosphatases involved in synthetic pathways usually have a high substrate specificity and are to be distinguished from nonspecific phosphatases which are essentially digestive enzymes (Chapter 12). 

A quantitatively much more important pathway of C02 fixation is the reductive pentose phosphate pathway (ribulose bisphosphate cycle or Calvin-Benson cycle Fig. 17-14). This sequence of reactions, which takes place in the chloroplasts of green plants and also in many chemiautotrophic bacteria, is essentially a way of reversing the oxidative pentose phosphate pathway (Fig. 17-8). The latter accomplishes the complete oxidation of glucose or of glucose 1-phosphate by NADP+ (Eq. 17-48) ... 

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