Bohr effect of human hemoglobin: Separation of tertiary and quaternary contributions based on the Wyman equation

Central venous oxygen saturation changes as a reliable predictor of the change of CI in septic shock: To explore potential influencing factors

PURPOSE

Assessing fluid responsiveness relying on central venous oxygen saturation (ScvO2) yields varied outcomes across several studies. This study aimed to determine the ability of the change in ScvO2 (ΔScvO2) to detect fluid responsiveness in ventilated septic shock patients and potential influencing factors.

METHODS

In this prospective, single-center study, all patients conducted from February 2023 to January 2024 received fluid challenge. Oxygen consumption was measured by indirect calorimetry, and fluid responsiveness was defined as an increase of cardiac index (CI) ≥ 10% measured by transthoracic echocardiography. Multivariate linear regression analysis was conducted to evaluate the impact of oxygen consumption, arterial oxygen saturation, CI, and hemoglobin on ScvO2 and its change before and after fluid challenge.

RESULTS

Among 49 patients (31 men, aged (59 ± 18) years), 27 were responders. The patients had an acute physiology and chronic health evaluation II score of 24 ± 8, a sequential organ failure assessment score of 11 ± 4, and a blood lactate level of (3.2 ± 3.1) mmol/L at enrollment. After the fluid challenge, the ΔScvO2 (mmHg) in the responders was greater than that in the non-responders (4 ± 6 vs. 1 ± 3, p = 0.019). Multivariate linear regression analysis suggested that CI was the only independent influencing factor of ScvO2, with R2 = 0.063, p = 0.008. After the fluid challenge, the change in CI became the only contributing factor to ΔScvO2 (R2 = 0.245, p < 0.001). ΔScvO2 had a good discriminatory ability for the responders and non-responders with a threshold of 4.4% (area under the curve = 0.732, p = 0.006).

CONCLUSION

ΔScvO2 served as a reliable surrogate marker for ΔCI and could be utilized to assess fluid responsiveness, given that the change of CI was the sole contributing factor to the ΔScvO2. In stable hemoglobin conditions, the absolute value of ScvO2 could serve as a monitoring indicator for adequate oxygen delivery independent of oxygen consumption.

Molecular Characterization of Carbonic Anhydrase Genes in Lotus japonicus and Their Potential Roles in Symbiotic Nitrogen Fixation

Carbonic anhydrase (CA) plays a vital role in photosynthetic tissues of higher plants, whereas its non-photosynthetic role in the symbiotic root nodule was rarely characterized. In this study, 13 CA genes were identified in the model legume Lotus japonicus by comparison with Arabidopsis CA genes. Using qPCR and promoter-reporter fusion methods, three previously identified nodule-enhanced CA genes (LjαCA2, LjαCA6, and LjβCA1) have been further characterized, which exhibit different spatiotemporal expression patterns during nodule development. LjαCA2 was expressed in the central infection zone of the mature nodule, including both infected and uninfected cells. LjαCA6 was restricted to the vascular bundle of the root and nodule. As for LjβCA1, it was expressed in most cell types of nodule primordia but only in peripheral cortical cells and uninfected cells of the mature nodule. Using CRISPR/Cas9 technology, the knockout of LjβCA1 or both LjαCA2 and its homolog, LjαCA1, did not result in abnormal symbiotic phenotype compared with the wild-type plants, suggesting that LjβCA1 or LjαCA1/2 are not essential for the nitrogen fixation under normal symbiotic conditions. Nevertheless, the nodule-enhanced expression patterns and the diverse distributions in different types of cells imply their potential functions during root nodule symbiosis, such as CO₂ fixation, N assimilation, and pH regulation, which await further investigations.

R and R2 quaternary structures of carbonmonoxyhemoglobins: Differential effect of inositol hexakisphosphate on their affinity for Ellman's reagent

The reaction of 5,5'-dithiobis(2-nitrobenzoate), DTNB, with hemoglobin sulfhydryl groups is linked to three negatively contributing Bohr effect groups: His2β is present in all avian hemoglobins but absent in some mammalian hemoglobins; His77β and His143β are absent in avian but present in nearly all mammalian hemoglobins. To probe the consequences of these differences, we determined the influence of inositol hexakisphosphate (inositol-P₆) on the DTNB affinities of avian and mammalian carbonmonoxyhemoglobins. Inositol-P₆decreases by two orders of magnitude the DTNB affinity of guinea pig hemoglobin, which has His2β and the R2 quaternary structure. It decreases, or has no effect on, the DTNB affinities of hemoglobins that have His2β and whose structures lie along the R2 ⇌ R quaternary equilibrium. Finally, inositol-P₆increases by one to two orders of magnitude the DTNB affinities of hemoglobins that lack His2β. Thus His2β, DTNB and inositol-P₆, in combination, distinguish the R2 from the R quaternary structure.

Bohr effect and oxygen affinity of carp, eel and human hemoglobin: Quantitative analyses provide rationale for the Root effect

The functional properties of most fish hemoglobins are more complex than those of human hemoglobin. This complexity arises in the form of the Root effect, in which the oxygen affinity of such fish hemoglobins decreases rapidly with pH relative to that of human hemoglobin. Cooperative ligand binding is also diminished below pH ≈ 6.5. The Bohr effect, determined by acid-base titration, has been reported for the Root effect carp and anodic eel hemoglobins. Unlike for mammalian hemoglobins, the Wyman equation for the Bohr effect fails to account quantitatively for these Bohr data. We present a successful quantitative accounting for these data based on evidence for multiple T states in various fish hemoglobins and on their lack of sixhistidine Bohr groups, with pK^oxy > pK^deoxy. On the same bases we also provide a rationale for the higher pH sensitivity of the oxygen affinity of carp compared to human hemoglobin.