Summary 1. Polyhedral bodies are present in several groups of autotrophic bacteria that assimilate inorganic carbon via the Calvin cycle, including members of the colourless sulphur‐ oxidizing bacteria, ammonia‐ and nitrite‐oxidizing bacteria and all cyanobacteria (blue‐green algae) examined. Other groups of Calvin‐cycle bacteria lack the inclusions, which have not been found in the purple photosynthetic bacteria, or in the hydrogen bacteria, with one exception in each case. Polyhedral bodies also occur in the chlorophyll b‐containing photosynthetic symbiotic prokaryote, Prochloron, and in several cyanelles. The inclusion bodies have not been found in prokaryotes that cannot fix carbon dioxide via the Calvin cycle, or in eukaryotes. 2. Polyhedral bodies have been isolated from a colourless sulphur bacterium (Thiobacillus neapolitanus), two nitrifying bacteria (Nitrobacter agilis and Nitrosomonas sp.) and two cyanobacteria (Anabaena cylindrica and Chlorogloeopsis fritschii). Ribulose 1,5‐bisphosphate carboxylase/oxygenase (RuBisCO), the carbon dioxide‐fixing enzyme of the Calvin cycle, has been found in the polyhedral bodies in each case, confirming that these inclusions in autotrophic bacteria be re‐termed carboxysomes. 3. Knowledge of carboxysome composition has been constrained by difficulties in carboxysome isolation, although effective methods, including cell disruption in low‐ionic‐strength buffers followed by density‐gradient centrifugation through silicon polymers, or sucrose, followed be preparative agarose electrophoresis, are now available. 4. Analysis of isolated T. neapolitanus, N. agilis and C. fritschii carboxysomes by dissociating sodium dodecyl sulphate‐polyacrylamide gel electrophoresis has revealed the presence of 7–15 polypeptides, the most abundant being the large and small subunits of RuBisCO. Two polypeptides of the T. neapolitanus carboxysomes have been ascribed to the carboxysome membrane (shell), although the identity of other polypeptides is unknown. 5. DNA of unknown function has been reported in carboxysomes isolated from two Nitrobacter species and may be present in the organelles from T. neapolitanus. 6. RuBisCO occurs in both the carboxysomes and in soluble form in the cytoplasm of carboxysome‐containing bacteria. Structural, kinetic, regulatory and immunological comparisons have demonstrated full or near identity between the cytoplasmic and carboxysomal forms of the enzyme. As with RuBisCO from chloroplasts and from almost all non‐carboxysome‐containing bacteria, the cytoplasmic and carboxysomal RuBisCOs each consist of eight large plus eight small subunits. All RuBisCOs are bifunctional enzymes, oxygen acting as a competitive inhibitor of carboxylation, and carbon dioxide acting competitively to inhibit the apparently wasteful oxygenase reaction. Carbon dioxide and oxygen fixation occur at the same site on the large subunit. Despite extensive study, the function of the small subunits is unknown. All RuBisCOs can exist in an inactive and active form, activation proceeding by an ord...

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2089The Calvin cycle enzyme phosphoribulokinase has been localized in terms of catalytic activity and enzyme protein in the cyanobacterium Chlorogloeopsis fritschii. In contrast to the C02-fixing enzyme of the Calvin cycle, o-ribulose-l,5-bisphosphate carboxylase/oxygenase (RuBisCO), which occurs in the cytoplasm and in the carboxysomes, phosphoribulokinase is essentially (95 %) cytoplasmic in extracts from cells grown photoautotrophically to late exponential phase.Total phosphoribulokinase accounted for 0.6% of total cell protein in these cells. Immunochemical identity was found between the phosphoribulokinase located in the cytoplasm and the remaining enzyme (5%) associated with the particulate fraction of the cell obtained following differential centrifugation. On density gradient centrifugation of the particulate fraction into Percoll plus sucrose the RuBisCO activity was located in a carboxysome band in the lower half of the gradient while the phosphoribulokinase activity essentially remained concentrated at the top of the gradient. Comparison of RuBisCO and phosphoribulokinase distributions suggests that the latter is not a carboxysomal enzyme in late exponential phase cells of C. fritschii.

Background Asthma is an example of a common, chronic illness in which clinicians are encouraged to promote concordance and adhere to guidelines. Some existing research suggests that these aims may be incompatible.

Electrophoretic techniques were used in an attempt to assess the degree of genetic differentiation among 2 Fucus species: -F. serratus and F. vesiculosus. One population of each species was surveyed for seven enzymes. Critical examination of the methods of detecting enzyme polymorphisms by electrophoresis showed that the value of the techniques äs used in this study is limited in the case of Fucus. This was due firstly to technical limitations: because of low enzyme activities it was necessary to use heavily loaded rods of polyacrylamide and these required long stain incubation times which allowed band diffusion. In addition some masking of isoenzyme mobility by slight Variation in gel composition occurred. Secondly, in this study no enzyme polymorphism on which to base alleie frequencies was unequivocally detected in populations of F. serratus and F. vesiculosus. Improvements in the techniques are outlined. Intrpduction