Properties of substituted 2-trifluoromethylbenzimidazoles as uncouplers of oxidative phosphorylation

1. The activity of 25 substituted 2-trifluoromethylbenzimidazoles in uncoupling oxidative phosphorylation by rat-liver mitochondria has been compared. 2. For halogen- or mixed-halogen- and alkyl-substituted analogues, uncoupling activity was proportional to the acidity of the imidazole -NH group. Tetrachloro-2-trifluoromethylbenzimidazole was the most active (50% uncoupling of oxidative phosphorylation at 7.9x10(-8)m, pK5.04). Nitro-substituted analogues were less active than predicted from pK considerations or from partition-coefficient measurements. 3. Introduction of an -NH(2) or -CO(2)H substitutent caused a loss of uncoupling activity, as did alkylation at position 1 of the imidazole ring. 4. Benzimidazoles active as uncouplers stimulated mitochondrial adenosine triphosphatase but not all stimulated the oxidation of succinate in the absence of a phosphate acceptor. 5. 4,5-Dichloro-2-trifluoromethylbenzimidazole inhibited the succinate-oxidase system at about the same concentration required for uncoupling (0.52mum for 50% inhibition of both activities) and the site of this inhibition appears to lie between succinate dehydrogenase and cytochrome b.     

Pulsed-field gel analysis of human immunoglobulin heavy-chain constant region gene deletions reveals the extent of unmapped regions within the locus

The human immunoglobulin heavy-chain constant region gene locus is organized in three main gene groups, the physical distances of which are unknown. Different types of gene deletions, originated by unequal crossingover, have been found to encompass one or more genes in the locus. We have analyzed some of these deletions by means of pulsed-field gel electrophoresis, which allows resolution of large DNA fragments. By identifying a fragment containing two of the main gene groups and by observing the size reduction of this fragment in subjects with deletions, we were able to estimate the distance between the two groups and better locate the pseudogene in-between.     

Characterization of an antibody-binding epitope from the 18-kDa protein on Mycobacterium leprae

A murine mAb, designated L5, appears to be specific for an epitope on a protein from Mycobacterium leprae of restricted distribution within the mycobacteria. This protein, of Mr 18,000 (18 kDa) is of interest because monoclonal antibodies raised against it do not appear to cross-react with other mycobacterial pathogens. The L5 antibody-binding epitope has been mapped by two complementary methods; expression of gene fragments and synthesis of short peptides. This L5-binding region of the 18-kDa protein (amino acids 109 to 115) shows some homology to a region of the GroEL heat shock family of proteins. Characterization of this antibody-binding epitope may lead to a reagent of use in early diagnosis of infection.     

Cytochemical properties of osteoblast cell membrane domains

The interactions of osteoblasts with one another and with the extracellular milieu are of vital importance for cell function. These interactions are mediated by cell membrane-associated components. In the present work, we studied the distribution of several mediators known to be associated with the cell surface, using ultrastructural cytochemistry, to characterize the three cell membrane domains (osteoid, lateral, and vascular) of osteoblasts. Osteoblasts in neonatal rat calvariae were studied for cell surface distribution of alkaline phosphatase (APase), calcium-activated adenosine triphosphatase (Ca2+-ATPase), calcium, soybean agglutinin (SBA)-reactive sites, and peanut agglutinin (PNA)-reactive sites. APase was absent in the osteoid domain but was evenly distributed in the other domains. Ca2+-ATPase was found to be concentrated mainly in the lateral domains. In contrast, calcium was present in all cell membrane domains. Using lectins conjugated to horseradish peroxidase, we demonstrated that SBA binding sites were evenly distributed along the osteoblast cell membrane, whereas PNA binding sites were absent or minimally present in the osteoid and lateral domains but were evenly distributed in the vascular domain. These results suggest that the various functions of osteoblasts may be facilitated by specialized cell membrane domains which are cytochemically distinct. Previous reports have failed to demonstrate the cytochemical differences between the three domains of the osteoblast cell membrane.