Inhibition of cyclic amp phosphodiesterase by 5'-deoxy-5'-S-isobutylthioadenosine at biologically active concentrations of drug

5'-Deoxy-5'-S-isobutylthioadenosine (SIBA), a synthetic analogue of S-adenosylhomocysteine, has been reported by others to inhibit a number of biological processes and these effects of SIBA have been attributed generally to inhibition of methyltransferases. However, the present studies with mouse lymphocytes show that SIBA also acts as a competitive inhibitor (K_i = 130 μM) of the high-affinity cyclic AMP phosphodiesterase and potentiates the cyclic AMP response of intact cells to several activators of adenylate cyclase. Moreover, SIBA has been found to inhibit lymphocyte-mediated cytolysis, a cellular function known to be sensitive to elevated lymphocyte levels of cyclic AMP, at concentrations (IC₅₀ = 250 μM) similar to those which inhibit cyclic AMP phosphodiesterase. These results indicate the need for caution in attributing biological effects of SIBA singularly to inhibition of methyltransferases and suggest the possible agency of cyclic AMP in the mechanism of SIBA action.     

Identification of Ia on a subpopulation of human T lymphocytes that stimulate in a mixed lymphocyte reaction

The delineation of discrete subpopulations of human T lymphocytes has permitted preliminary analyses of the complex cellular network regulating the immune response in man. We previously showed that a subset of T lymphocytes, designated as theophylline-sensitive because of their inability to bind sheep red blood cells in the presence of the drug, are responsible for antigen-specific suppression or regulation in an in vitro plaque-forming cell assay. We now show that 25 to 45% of these theophylline-sensitive T cells were Ia-positive by immunofluorescence with a rabbit antiserum raised against purified B lymphoblast surface antigenic material. These data suggested that 4 to 7% of peripheral blood T cells carry Ia determinants. The presence of Ia determinants on this T cell subset was confirmed by gel analysis of radioiodinated surface material. Furthermore, in mixed lymphocyte culture, the theophylline-sensitive cells demonstrated HLA-D determinants and were 10-fold more potent stimulators than equal numbers of B lymphocytes. The presence of Ia determinants on these T cells indicates the expression of major histocompatibility complex-related regulatory gene products on a specific human T lymphocyte subpopulation.     

Metabolic formation of nucleoside-modified analogues of S-adenosylmethionine

A Pseudo-ovalbumin gene, bearing significant nucleotide sequence homology to the ovalbumin gene, has been cloned from genomic chick DNA. Similar to the authentic ovalbumin gene, the pseudo-gene is a unique sequence gene in the chick genome and is expressed at a low level in the immature chick oviduct. In contrast to the ovalbumin gene, expression of the pseudo-gene in the oviduct is not inducible by estrogen. The concentration of pseudo-gene RNA is only ～0.01% of that of authentic ovalbumin mRNA in estrogen-stimulated oviduct cells. Nucleotide sequence analysis of the two sequence related genes may reveal the molecular basis of differential response to steroid hormone induction in the same tissue.     

Immunological and biochemical characterization of nuclear envelope reduced nicotinamide adenine dinucleotide phosphate-cytochrome c oxidoreductase.

NADPH-cytochrome c oxidoreductase (EC 1.6.99.2) activity innate to rat liver nuclear envelope displays antigenic identity with the corresponding microsomal enzyme in a standard Ouchterlony double immunodiffusion test. As with the microsomal enzyme, the nuclear envelope enzyme is selectively released by restricted proteolysis and may be quantitatively isolated from the supernatant phase of the digest by immunoprecipitation. Sodium dodecyl sulfate-polyacrylamide gel electrophoretic analysis of the immunoprecipitates reveals that the oxidoreductase has a molecular weight of 72,000 regardless of its membrane of origin. Radial immunodiffusion titration demonstrates that nuclear envelope contains about one-third the level of NADPH-cytochrome c oxidoreductase (0.21%) as compared to microsomal membrane (0.71%) on a weight basis. By comparison, the specific activity of the nuclear envelope enzyme was half that of the microsomal enzyme. Turnover studies employing NaH¹⁴CO₃ indicate that the half-lives for the nuclear envelope and microsomal enzymes are indistinguishable, each being approximately 55 h.     

Lipoxygenase and hydroperoxide lyase in germinating watermelon seedlings

Lipoxygenase (EC 1.13.1.13) was found in seedlings of Citrullus lanatus (Thunb.) Matsum. and Nakai (watermelon). The enzyme has pH optima of 4.4 and 5.5 and is inhibited by 0.2 mM nordihydroguaiaretic acid. It is present in two functional units with estimated molecular weights of 120,000 and 240,000, respectively.     

A DNA ligase from mitochondria of rat liver.

An ATP-dependent DNA ligase has been demonstrated in extracts of rat liver mitochondria. The activity may be released from the mitochondria by treatment with hypotonic solutions or a detergent, indicating an intramitochondrial localization. The properties of the partially purified enzyme are similar to those of the nuclear DNA ligase from rat liver.     

Comparative zone electrophoresis of catalase of Staphylococcus species isolated from mammalian skin.

Vertical polyacrylamide slab gel electrophoresis was conducted for the catalase enzymes of representative strains of 18 proposed species and subspecies of the genus Staphylococcus. The catalase bands which resulted were predominantly monomorphic within each of the species and differences in catalase mobilities were observed between many of the species. The electrophoretic mobilities of the catalases were supportive to the scheme of classification used. Many strains of certain species demonstrated multiple catalase bands which are suggestive of multimolecular forms of the enzyme. Horizontal starch gel electrophoresis of representative strains of S. capitis produced catalase bands with relative mobilities that were different from those obtained with polyacrylamide electrophoresis, presumably due to a difference in molecular sieving between the gels.     

Species density and associations in Caribbean reef corals

The density of scleractinian corals on portions of two reefs in the Grenadine Islands, W. I. has been investigated by direct observation by SCUBA divers. Grid, transect, and random quadrat methods were compared with total samples to determine the precision and accuracy of these techniques. Transect methods were generally satisfactory provided at least 15% of a 400 m² total grid area was included in the sample. The data strongly indicated clumped distributions of all species, although numerical analysis does not indicate the distinct zones reported by other workers. Species associations based on Jaccard's coefficient and cluster analysis showed possible similarities in physical requirements, although few strong associations were found. Data based on 4 m² quadrats generally provided a more reliable estimate of species associations than did data based on 1 m² quadrats. It is suggested that surveys of these reef types may be better based on a number of parallel transects rather than a single transect, and that well-defined zones are more likely to be the exception than the rule.