Identification of protein side chains near the membrane-aqueous interface: a site-directed spin labeling study of KcsA.

This study presents an approach to identifying surface residues on membrane proteins that are exposed toward the membrane-aqueous interface. The method employs a lipid Ni(II) chelate that localizes the metal ion to a region near the membrane-aqueous interface. Lateral diffusion of the lipid chelate results in Heisenberg exchange (HE) with nitroxide side chains in the protein only if direct contact occurs between the paramagnetic species during a collision. Thus, HE serves as a signature for residues facing the bilayer in the neighborhood of the membrane-aqueous interface. To evaluate the method, 13 surface residues on the extracellular half of KcsA, a prokaryotic potassium channel of known structure, were examined for HE with the Ni(II) chelate. The HE rate between the two species is found to depend strongly on the vertical position of the nitroxide with respect to the membrane-aqueous interface. Nitroxides introduced near the interface experience relatively high HE rates, whereas nitroxides that are immersed in the bilayer interior or sterically sheltered from collision experience low or undetectable rates. The results indicate that residues near the interface can be identified on the basis of their high rates of collision with the headgroup region of the bilayer.     

Respiratory components in acidophilic bacteria that respire on iron

Abstract

Microorganisms capable of aerobic respiration on ferrous ions are spread throughout eubacterial and archaebacterial phyla. Phylogenetically distinct organisms were shown to express spectrally distinct redox‐active biomolecules during autotrophic growth on soluble iron. A new iron‐oxidizing eubacterium, designated as strain Funis, was investigated. Strain Funis was judged to be different from other known iron‐oxidizing bacteria on the bases of comparative lipid analyses, 16S rRNA sequence analyses, and cytochrome composition studies. When grown autotrophically on ferrous ions, Funis produced conspicuous levels of a novel acid‐stable, acid‐soluble yellow cytochrome with a distinctive absorbance peak at 579 nm in the reduced state.

Stopped‐flow spectrophotometric kinetic studies were conducted on respiratory chain components isolated from cell‐free extracts of Thiobacillus ferrooxidans. Experimental results were consistent with a model where the primary oxidant of ferrous ions is a highly aggregated c‐type cytochrome that then reduces the periplasmic rusticyanin. The Fe(II)‐dependent, cytochrome c‐catalyzed reduction of the rusticyanin possessed three kinetic properties in common with corresponding intact cells that respire on iron: the same anion specificity, a similar dependence of the rate on the concentration of ferrous ions, and similar rates at saturating concentrations of ferrous ions     

Recurrence after surgical treatment of hidradenitis suppurativa.

From six to 89 months after surgery 82 patients who had been treated by radical surgery (118 excisions) for intractable hidradenitis suppurativa were reviewed. Local recurrence rates varied greatly with the disease site, being low after axillary (3%) and perianal surgery (0%) and high after inguinoperineal (37%) and submammary (50%) excision. Recurrence results from inadequate excision or an unusually wide distribution of apocrine glands, but physical factors such as obesity, local pressure, and skin maceration played a part in a few patients. Recurrence due to inadequate surgery tended to be the most troublesome. At follow up 75 (91%) of the patients were pleased with the results of their operation. A quarter of the patients developed disease at a new anatomical site after operation. Radical surgery gives good symptomatic control of severe hidradenitis suppurativa of the axilla, inguinoperineal, and perianal regions but is less satisfactory for submammary disease.