Human debrisoquine 4-hydroxylase (P450IID1): cDNA and deduced amino acid sequence and assignment of the CYP2D locus to chromosome 22

The enzyme P450db1 (db1) is responsible for the common human defect in drug oxidation known as the "debrisoquine/sparteine polymorphism." Polyclonal antibody against the rat db1 protein was used to screen a human liver lambda gt11 library for the db1 cDNA clone. A cDNA containing the full protein coding sequence was isolated; the deduced NH2-terminal sequence of this cDNA was identical to that derived from direct sequencing of the purified human db1 protein. Comparison of the human db1 with rat db1 revealed 71 and 73% similarities of nucleotides and amino acids, respectively. By use of human-rodent somatic cell hybrids the db1 gene was localized to human chromosome 22 (CYP2D locus).     

Nonequivalent effects of PKC activation by PMA on murine CD4 and CD8 cell-surface expression

The membrane glycoproteins CD4 (L3T4) and CD8 (Lyt2) are expressed on distinct populations of mature murine T lymphocytes, and are thought to be receptors for monomorphic determinants expressed on MHC class II and class I molecules, respectively. Although they differ in their ligand specificity, it has been presumed that CD4 and CD8 perform equivalent functions in the T cells that bear them. Since activation of protein kinase C (PKC) is known to cause rapid down-regulation of various receptors, including the T cell receptor complex (TcR complex), we treated cells with phorbol 12-myristate 13-acetate (PMA), a PKC activator, to determine whether cell-surface expression of CD4 and CD8 would be similarly affected by this intracellular mediator. Brief or relatively prolonged treatment with PMA induced mature murine T cells to reduce their surface expression of the TcR complex and of CD4, but not of CD8. Similarly, PMA rapidly induced transfected L cells to down-regulate surface CD4 expression, but had no effect on surface CD8 expression. Most significantly, PMA treatment induced CD4+CD8+ immature thymocytes to rapidly reduce their surface CD4 expression, but, again, it had no immediate effect on the surface expression of CD8. These results indicate that CD4 and TcR complex cell-surface expression are both sensitive to PKC activation by brief treatment with PMA, whereas CD8 expression is not, and suggest that CD4 and CD8 surface expression levels are regulated by distinct intracellular mechanisms.     

Nucleotide sequence of Acinetobacter baumannii aphA-6 gene: evolutionary and functional implications of sequence homologies with nucleotide-binding proteins, kinases and other aminoglycoside-modifying enzymes

A new kanamycin-resistance gene, detected in Acinetobacter baumannii and designated aphA-6, was sequenced. It specifies a 30319 Dalton 3'-aminoglycoside phosphotransferase (APH(3'] that mediates resistance to kanamycin and structurally related aminoglycosides, including amikacin. Pairwise comparisons of the six types of APH(3') so far detected in human pathogens (types I, II, III and VI) and in amino-glycoside-producing microorganisms (types IV and V), confirm that APH(3') enzymes have diverged from a common ancestor. Three highly retained motifs (1: V--HGD----N; 2: G--D-GR/K-G and 3: D--K/R--Y/F---LDE) located in the C-terminal part of the enzymes were defined. Screening of protein sequence data bases fore each of these motifs revealed that motifs 1 and 2 are both found in nucleotide-binding phosphotransferases associated with a variety of biological processes, namely adenylate kinase, viral oncogenic protein kinases, elongation factors, Na+/K+-transporting ATPase, myosin and antibiotic-modifying enzymes. Motif 2 probably corresponds to the MgATP binding site, while motifs 3 and 1 could be involved in the splitting of the phosphodiester bond and in the phosphate transfer, respectively. Moreover, an additional motif, almost invariably centrally located, was found in all aminoglycoside-modifying enzymes. The occurrence of this motif, possibly a recombination site which would have allowed the association of units of separate functions, is compatible with a modular concept for the structure of aminoglycoside-modifying enzymes.     

Should colonoscopy be the first investigation for colonic disease?

Many patients with suspected colonic disease undergo rigid sigmoidoscopy, barium enema examination, and ultimately total colonoscopy, but the need for preliminary radiology has not been formally assessed. A total of 168 patients requiring large bowel investigation were therefore randomised to undergo either rigid sigmoidoscopy plus double contrast barium enema examination or total colonoscopy. Disease was found in 56 patients, including 14 with a carcinoma, 11 with polyps, and 16 with inflammatory bowel disease, the remainder having diverticular disease alone. Of the 89 patients allocated to double contrast barium enema examination, nine required a subsequent colonoscopy for suspected tumour or polyps, three because of incomplete radiological examination, and 12 for rectal bleeding for which no cause was found at the radiological examination. In 16 patients this yielded further information or altered treatment. Of the 79 patients undergoing total colonoscopy, only six required subsequent radiology.As both procedures were well tolerated with no major complications total colonoscopy may be the preferred initial investigation where facilities allow.     

A scanning and transmission electron microscopic study of the lung of a caecilian Boulengerula taitanus

The lung of an apodan amphibian Bouiengerula taitanus has been investigated by scanning and transmission electron microscopy. This caecilian has only a single, long tubular lung that tapers towards the caudal end of the body. The lung has a central air duct which radially opens into a single stratum of alveoli lined by well developed septa that attach to two diametrically opposite trabeculae. The trabeculae carry the pulmonary artery and vein. The septa have blood capillaries on both surfaces and supportive and contractile elements like collagen, smooth muscle, elastic tissue and fibrocytes. The alveolar surface has only a single population of pneumocytes that combine the morphological features of the mammalian type 1 and 2 cells, i.e. they contain the osmiophilic, lamellated bodies and are squamous in form. Through subepithelial cytoplasmic invaginations, the pneumocytes, together with their basement lamina, were observed to be firmly attached to the septa1 tissue elements, presumably to avoid mechanical detachment during the rapid respiratory movements. The compartmentation of the whole lung in this species is viewed as a means of increasing the surface area available for gas exchange which, coupled with other already established cardiovascular adaptations in this species, may be of significance in its fossorial mode of life, an environment that is usually hypoxic and hypercarbic.     

Mechanisms of tetracycline and rifampicin resistance inBacteroides fragilis mutants obtained by ionizing radiation

Summary Based on a dose-survival curve, a radiation dose of 3.99 C/kg was used to induce antibiotic-resistant mutants inBacteroides fragilis. Escherichia coli B/r membrane fragments were employed as a reducing agent. Antibiotic-resistant mutants ofB. fragilis were utilized to study the mechanism by which these organisms become resistant to selected chemotherapeutic agents. Decreased accumulation of tetracycline by resistant mutants ofB. fragilis suggests that the resistance to this antibiotic is associated with the outer membrane permeability. There is a marked difference in the inhibitory action of rifampicin on RNA polymerase activity in rifampicin-sensitive and-resistant strains ofB. fragilis. This enzyme is, therefore, the likely target for inhibition of bacterial growth in this anaerobe by rifampicin.