Differences in superoxide production by nonmigrating and migrating human monocyte subpopulations

Human peripheral blood monocytes comprise two subpopulations. Whereas one subpopulation migrates to a variety of chemoattractants $\text{in}\text{vitro}$, the remaining subpopulation fails to respond to chemoattractants. The subpopulations were isolated with a chemotaxis separation chamber and their superoxide generation was studied. Superoxide production was continuously monitored during monocyte exposure to phorbol myristate acetate, N-formyl-methionyl-leucyl-phenylalanine and N-formyl-norleucyl-leucyl-phenylalanine. Superoxide production by nonmigrating monocytes was less than 33% of the migrating subpopulations' production. Thus, the subpopulation of monocytes which fails to migrate to chemoattractants also demonstrates defective superoxide production.     

The effect of detergents and lipids on the properties of the outer-membrane protein OmcA from Shewanella oneidensis

The protein OmcA from the bacterium Shewanella oneidensis was purified to homogeneity, and characterized using UV–vis spectroelectrochemistry, EPR, and circular dichroism (far- and near-UV regions). EPR spectroscopy showed that many different c-type hemes are present in the protein: high-spin, low-spin, and highly anisotropic low-spin hemes were all detected. The protein was shown to bind tightly to artificial membranes (liposomes) composed of dioleoylphosphatidylglycerol and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (60:40 molar ratio), which mimic the natural environment. However, on the basis of the spectroscopic and electrochemical studies, binding to liposomes does not appear to significantly alter either the structure or the properties of OmcA. On the other hand, the electrochemical properties of OmcA are noticeably changed in the presence of the detergents used during the initial purification stages. In particular, the reduction potentials of two out of the ten OmcA hemes appear to shift in the presence of detergent, perhaps because these hemes are solvent-exposed.