PubMed · 732656
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F O Stephens, P H Jones. 1978-12-16. Laser surgery.. https://doi.org/10.5694/j.1326-5377.1978.tb131755.x
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This retrospective study of 104 New York Heart Association class 1 to 4 heart failure patients undergoing exercise stress testing with gas exchange analysis demonstrated that the ventilatory equivalent for carbon dioxide at anaerobic threshold is useful in determining prognosis in patients with severe congestive heart failure, particularly when used in combination with peak exercise oxygen consumption. A ventilatory equivalent for carbon dioxide >50 and peak oxygen consumption < or =15.0 ml/kg/min defines a very high-risk patient group who should be prioritized for transplantation.
Strongly carboxylase-specific ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) was found in Galdieria partita and Cyanidium caldarium (Cyanidiophyceae). The relative specificity, VcKo/VoKc, of Galdieria and Cyanidium RuBisCO was 238 and 222, respectively; 2.4 to 2.5-fold that of higher plant RuBisCOs. The apparent Km of RuBisCO from the thermophilic red algae for CO2 was 6 to 7 microM and the smallest of the values reported so far for other RuBisCOs. The pre-rhodophyte Porphiridium purpureum, which lives at moderate temperatures, had RuBisCO with the relative specificity value of 144. A large difference (5.2 kcal x mol(-1)) in the activation energies between the carboxylase and oxygenase activities in Galdieria RuBisCO was a cause of the strong specificity for the carboxylase activity.
Chloroplast carbonic anhydrase is dependent on a reducing environment to retain its catalytic activity. To investigate the properties of the three accessible cysteine residues of pea carbonic anhydrase, mutants were made in which Ala or Ser substituted for C165, C269, and C272. The mutants at position 165 were found to be spectroscopically similarly to the wild-type. They have a high catalytic activity, and are also sensitive to oxidation. In contrast, both C269 and C272 were found to be critical both for the structure and for the catalytic activity. All mutants with substitutions at either of these two positions had to be co-overexpressed with GroES/EL chaperones to give soluble enzyme in Escherichia coli. The k(cat) values were decreased by 2 and 3 orders of magnitude for the C272A and C269A mutants, respectively, and the Km values were increased approximately 7 times. However, the binding of the inhibitor ethoxyzolamide was only slightly weakened. The near-UV CD spectra were found to be changed in both sign and intensity compared to that of the wild-type, and the far-UV spectra indicate some loss of alpha-helix structure. Moreover, the quaternary structure was changed from the wild-type octameric to tetrameric in these mutants. The results indicate that mutation of either of these cysteines causes minor structural changes around at least one of the two tryptophans of the subunit. Furthermore, the data demonstrate that C269 and C272 are involved in the interaction between subunits and are necessary for a proper structure at the tetramer-tetramer interface.