The iron dispersion of the globular cluster M2, revised

M2 has been claimed to possess three distinct stellar components that are enhanced in iron relative to each other. We use equivalent width measurements from 14 red giant branch stars from which Yong et al. detect a ∼0.8 dex wide, trimodal iron distribution to redetermine the metallicity of the cluster. In contrast to Yong et al., which derive atmospheric parameters following only the classical spectroscopic approach, we perform the chemical analysis using three different methods to constrain effective temperatures and surface gravities. When atmospheric parameters are derived spectroscopically, we measure a trimodal metallicity distribution, that well resembles that by Yong et al. We find that the metallicity distribution from Fe ii lines strongly differs from the distribution obtained from Fe i features when photometric gravities are adopted. The Fe i distribution mimics the metallicity distribution obtained using spectroscopic parameters, while the Fe ii shows the presence of only two stellar groups with metallicity [Fe/H] ≃ -1.5 and -1.1 dex, which are internally homogeneous in iron. This finding, when coupled with the high-resolution photometric evidence, demonstrates that M2 is composed by a dominant population (∼99 per cent) homogeneous in iron and a minority component (∼1 per cent) enriched in iron with respect to the main cluster population.

[Predictive near-infrared SLO signs for tears of the retinal pigment epithelium due to age-related macular degeneration]

PURPOSE

The aim of this study was to identify potential predictive markers in confocal scanning laser ophthalmoscopy (cSLO)-based imaging for tears of the retinal pigment epithelium (RPE) in the presence of pigment epithelial detachments (PED) due to age-related macular degeneration (AMD).

METHODS

Fifteen eyes of 15 patients (mean age 77 years, SD ± 6) with RPE tears and pre-existing PEDs were retrospectively analysed for the presence of increased signals on near-infrared imaging (NIR) using confocal scanning laser ophthalmoscopy (cSLO).

RESULTS

In 87 % of the cases increased reflectance signals on NIR in the area of the PED were noted prior to the development of an RPE tear. On average, these signals were recorded 58 days (SD ± 40) before the rip was diagnosed. In 62 % of the patients these signals were localised opposite to the rip location at the rim of the PED.

CONCLUSION

Increased reflectance signals on NIR imaging may serve as a predictive marker for RPE tears in patients with PED in AMD. These signals recordable with a non-invasive imaging method should be prospectively validated in a larger cohort of patients with PEDs. It may be useful in the management of patients exhibiting this manifestation of exudative AMD.

Structural characterization of the isoenzymatic forms of human myeloperoxidase: evaluation of the iron-containing prosthetic group

Myeloperoxidase (MPO) from human neutrophils has been purified and found to exist in three isoenzymatic forms, resolved by ion exchange chromatography. In addition to differences in subunit size and cellular compartmentalization of the isoenzymes, differences have been reported in their activity and susceptibility to inhibition. The structural basis of these isoenzymes is unclear; we attempted to further define their functional characteristics and structural identity. First, we measured respective enzymatic activity using a panel of substrates; MPO I was found to have lower activity with some substrates (pyrogallol, guaiacol, potassium iodide [KI]), but similar activity to the other isoenzymes with 4-aminoantipyrine. These studies confirm that MPO I is enzymatically distinct from MPO II and MPO III. Next, we examined the structural basis of these differences by evaluating the iron-containing prosthetic group in each form using electron paramagnetic resonance (EPR) and determination of the pyridine hemochrome. No significant difference between the isoenzymes was noted in these parameters, suggesting that the prosthetic group is the same in each protein. The cause for any difference in enzymatic activity must lie then in variations extrinsic to the heme, and based on previous studies of the gene and protein analysis, the posttranslational modification of MPO must account for these isoenzymatic species.