Characterization of a novel 14 kDa bile acid-binding protein from rat ileal cytosol

A 14 kDa polypeptide in rat ileal cytosol has been identified as the major intestinal cytosolic bile acid-binding protein (I-BABP) by photoaffinity labeling with the radiolabeled 7,7-azo derivative of taurocholate (7,7-azo-TC). To further characterize I-BABP, the protein was purified by lysylglycocholate Sepharose 4B affinity and DE-52 anion-exchange chromatography. The purified I-BABP contained a single 14 kDa band on SDS-PAGE. The 14 kDa protein showed a 26-fold increase in binding affinity for [3H]7,7-azo-TC compared to cytosolic protein. Immunoblotting of protein fractions separated by affinity chromatography showed that neither liver fatty acid binding protein (L-FABP) nor intestinal fatty acid binding protein (I-FABP) bind to the affinity column and that the 14 kDa protein which bound to the column and was subsequently eluted with detergent did not cross-react with anti-L-FABP or anti-I-FABP. The 14 kDa protein labeled with [3H]7,7-azo-TC was radioimmunoprecipitated from cytosol by rabbit antiserum raised against purified I-BABP. I-BABP was shown to have a blocked N-terminus; however, its mixed internal sequence generated from cyanogen bromide-cleaved protein and amino acid composition indicated that it was related to (although clearly distinct from) both I-FABP and L-FABP. These studies have isolated a 14 kDa bile acid-binding protein from rat ileal cytosol which is immunologically and biochemically distinct from I-FABP and L-FABP.     

Bacterial classification: an overview

Classification of bacteria evolved from limited subjective groupings to general, more objective arrangements based on overall phenotypic similarities. However, classifications based on phenotypic characters lack stability, whereas those based on genetic relatedness tend to be stable. DNA-DNA hybridization has proven to be extremely useful in resolving taxonomic problems at the species level. Broad relationships among bacteria have been identified by comparing ribosomal RNA cistrons; however, many groups based on ribosomal RNA analysis are not easily definable in terms of phenotypic similarities. Unless resolved, these problems could lead to the establishment of two separate classification systems, one phylogenetic and the other practical.     

Chemoreceptor function and metabolism of the carotid body in the rat

Using fluorimetric and polarographic determination of cell respiration, metabolic reactions of the carotid body of rats to adequate stimulation have been revealed. Functional relationships of the dose--effect type, which were found for these reactions, may be approximated by equations which are similar to those describing the unconditioned reflexes from the carotid chemoreceptors. However, reactions of the metabolics systems of the carotid body account for the perception of not all chemical stimuli, but only of acids and some alkaloids. These data reveal the heteregeneity of the carotid chemosensory system not only in the amphibians (which was known earlier), but in mammals as well.