To provide insight into the iron(IV)hydroxide
pKa of histidine ligated heme proteins,
we have probed the
active site of myoglobin compound II over the pH range of 3.9–9.5,
using EXAFS, Mössbauer, and resonance Raman spectroscopies.
We find no indication of ferryl protonation over this pH range, allowing
us to set an upper limit of 2.7 on the iron(IV)hydroxide pKa in myoglobin. Together with the recent determination
of an iron(IV)hydroxide pKa ∼ 12
in the thiolate-ligated heme enzyme cytochrome P450, this result provides
insight into Nature’s ability to tune catalytic function through
its choice of axial ligand.
We report on the protonation state of Helicobacter pylori catalase compound II. UV/visible, Mössbauer, and X-ray absorption spectroscopies have been used to examine the intermediate from pH 5 to 14. We have determined that HPC-II exists in an iron(IV) hydroxide state up to pH 11. Above this pH, the iron(IV) hydroxide complex transitions to a new species (pKa = 13.1) with Mössbauer parameters that are indicative of an iron(IV)-oxo intermediate. Recently, we discussed a role for an elevated compound II pKa in diminishing the compound I reduction potential. This has the effect of shifting the thermodynamic landscape toward the two-electron chemistry that is critical for catalase function. In catalase, a diminished potential would increase the selectivity for peroxide disproportionation over off-pathway one-electron chemistry, reducing the buildup of the inactive compound II state and reducing the need for energetically expensive electron donor molecules.
Objective: Critically ill older adults greater than or equal to 80 years old are routinely admitted to contemporary cardiac intensive care units (CICU). Little has been reported about their outcomes when compared to the general CICU population. The primary aim of this study was to compare the mortality, length-of-stay, and disposition outcomes of elderly patients (greater or equal to 80 years old) admitted to the CICU with a younger cohort (less than 80 years old).
Methods and Results: A single-center, retrospective cohort study was conducted including 6,194 adult patients admitted to a cardiovascular intensive care unit in Newark, Delaware, from July 1, 2012, to June 30, 2019. Coronary intensive care unit (CICU) mortality, CICU length-of-stay and discharge disposition were compared between elderly patients (greater than or equal to 80 years old) and younger patients (less than 80 years old), adjusted for comorbidities.
We observed increased mortality for elderly patients (OR 1.686, CI 1.361-2.090, p<0.001) compared with patients less than 80 years old, even after adjusting for comorbidities. Median length of stay was not statistically different between the two groups. However, the elderly patients were significantly more likely to be discharged to a facility, such as a skilled nursing facility, than those less than 80 years old (26.8% versus 12.5%, respectively, p<0.001).
Conclusions: Among patients admitted to the CICU, elderly patients have higher mortality rates than those less than 80 years old. Advanced age (greater or equal to 80 years old) was not a reliable predictor of outcome in the CICU. A large proportion of elderly patients are not able to live independently at home after CICU admissions.
Key Words: octogenarians, nonagenarians, cardiac intensive care unit, elderly, ICU mortality
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