Desensitization of beta-adrenergic stimulated adenylate cyclase in turkey erythrocytes.

Desensitization of catecholamine stimulated adenylate cyclase (AC) activity is demonstrated in membranes derived from turkey erythrocytes pre-treated with isoproterenol. Membranes from desensitized cells had a loss in maximal catecholamine stimulated adenylate cyclase activity of 104 +/- 13 (pmols/mg protein/10', p less than .001) compared with controls. When adenylate cyclase was maximally stimulated with NaF or Gpp(NH)p, the decrements were 84 +/- 19 (p less than .005) and 92 +/- 32 (p less than .05) pmol/mg protein/10' respectively. There was no change in beta-adrenergic receptor number in membranes derived from treated cells. While the molecular mechanism accounting for the desensitization is uncertain, the data is consistent with the hypothesis that there is a lesion distal to the beta-adrenergic receptor, possibly involving the nucleotide site or the catalytic subunit of adenylate cyclase, causing the desensitization in the isoproterenol treated cells.     

Reversion to methionine independence by malignant rat and SV40-transformed human fibroblasts.

Although many lines of malignant and transformed cells are unable to grow in folate- and cobalamin-supplemented medium in which methionine is replaced by homocysteine its immediate metabolic precursor, rare cells from these lines regained the normal ability to grow under these conditions. Six revertant lines, one from Walker-256 rat breast carcinoma cells and five from SV40-transformed human fibroblasts, have been characterized with regard to growth and three measures of methionine biosynthetic capacity: methionine synthetase and methylenetetrahydrofolate reductase activities in cell extracts, and uptake of label from [5-¹⁴C]methyltetrahydrofolate by intact cells. When all three measures of methionine biosynthetic capacity were considered, two revertants isolated from SV40-transformed cells had regained the ability to grow like normal cells in homocysteine medium without substantial changes in these measures. Increased methionine biosynthesis thus is not a prerequisite to reversion of the methionine auxotrophy present in the transformed parental lines.     

Structural studies of the polysaccharide antigen of Eubacterium saburreum, Strain L 32

The structure of the polysaccharide antigen produced by Eubacterium saburreum, strain L 32, has been investigated. The principal methods used were methylation analysis, graded hydrolysis with acid, and n.m.r. spectroscopy. The polysaccharide, which contains the unusual sugar 3,6-dideoxy-D-arabino-hexose (tyvelose, Tyv), is composed of trisaccharide repeating-units having the following structure:

     

Stimulatory effect of dihydroxyphenyl compounds on the aerotolerance of Spirillum volutans and Campylobacter fetus subspecies jejuni.

The aerotolerance of the microaerophilic bacterium Spirillum volutans was greatly stimulated in a defined medium by the presence of dihydroxyphenyl ferric iron-binding compounds such as nor-epinephrine at 10(-5) to 10(-6) M. Dihydroxyphenyl compounds at 2 X 10(-4) M, or iron salts (ferrous or ferric) at high concentration, greatly increased the aerotolerance of a strain of Campylobacter fetus subsp. jejuni when grown on streak plates of Brucella agar. The results suggest that the microaerophilism of these organisms might in part be caused by a failure to synthesize microbial ferric iron-binding compounds at sufficient levels to support aerobic growth.     

Electron-nuclear double resonance in melanins.

Electron-nuclear double resonance (ENDOR) signals from matrix protons interacting with the stable free radicals of "A"- and "B"-type melanins have been observed as a function of pH. In all samples the single line is similar in width and unusually narrow. The ENDOR reduction varies by more than a factor of 10, indicating a large sensitivity of relaxation properties of melanin to sample type. Signals were observed over a wide range of experimental conditions with good signal-to-noise ratio, establishing feasibility for further more detailed ENDOR studies. Incubation in D2O resulted in little change, indicating that the free radical is well buried or protected. No resolved hyperfine structure was seen, consistent with the generally accepted view that melanin is a heterogeneous polymer.     

Structural studies of the polysaccharide antigen of Eubacterium saburreum, strain 49.

The polysaccharide antigen produced by Eubacterium saburreum, strain L 49, is composed of D-glycero-D-galacto-heptose and a new sugar, tentatively identified as 6-deoxy-D-altro-heptose. It contains chains of alternating (1 leads to 3)- and (1 leads to 6)- linked beta-D-glycero-D-galacto-heptopyranosyl residues, the latter being substituted with 6-deoxy-alpha-heptofuranosyl groups at O-3. The polysaccharide further contains 0-acetyl groups, linked to O-7 of part of the heptosyl residues and to O-2 of part of the 6-deoxyheptosyl groups.     

Effects of Mg and Ca on the side dependencies of Na and K on ouabain binding to red blood cell ghosts and the control of Na transport by internal Mg

The effect of alteration in the concentration of internal Mg on the rate of ouabain binding to reconstituted human red blood cell ghosts has been evaluated as well as the effect of Mgi on Na:Na compared to Na:K exchange. It was found that the dependence of the rate of ATP-promoted ouabain binding on the combined presence of Nai and Ko which occurs at high [Mg]i is lost when the concentration of Mgi is lowered. The sensitivity of the external surface for Ko is also changed since Ko can now inhibit the ouabain binding rate in the absence of Nai; on the other hand Nao at low [Mg]i can stimulate ouabain binding indicating that the relative affinity of the outside surface for Nao has either increased or that for Ko has decreased or both. Thus the effects of changes in [Mg]i result in a change in the side-dependent actions of Na and K and emphasize the possible difficulties of interpreting results obtained on systems lacking sidedness. Mgi was found to be required for Pi-promoted ouabain binding and that the inhibitory action of Nai increased as [Mg]i was increased. In addition, Ca was found to be most effective in inhibiting the rate of ATP-promoted ouabain binding when Na and K were present together than when either was present alone. Na:K exchange was found to be more sensitive to the concentration of Mgi than Na:Na exchange; at low [Mg]i Na:K exchange could be stimulated without changing the extent of Na:Na exchange. These results are consistent with the idea that conformational states of the pump complex are directly influenced by [Mg]i.