Solvent-accessible surfaces of nucleic acids

Static solvent-accessible surface areas were calculated for DNA and RNA double helices of varied conformation, composition and sequence, for the single helix of poly(rC), and for a transfer RNA. The results show that for DNA and RNA double helices, two thirds of the water-accessible surface area become buried on double helix formation; phosphate oxygens retain near maximal exposure while the bases are 80% buried. Transfer RNA exposes slightly less surface per residue than does double-helical RNA, despite the presence of several additional “modified” groups, all of which are exposed significantly.When a probe corresponding to a single water molecule is used, both the total and atom type exposures are very similar for A-DNA and B-DNA, although marked differences appear in the major and minor groove exposures between the two conformations. For a given base-pair, the accessible surface area buried upon double-helical stacking is nearly constant (within 5%) for different sequences of neighboring base-pairs.For probes larger than single water molecules, there exist considerable differences in the total and atom type exposures of A-DNA and B-DNA. Conformational transitions between the A-DNA and B-DNA helical forms can thus be related to differences in the accessible areas for “structured” water, or a secondary hydration shell, rather than to interactions with individual water molecules of the primary hydration shell. The base-composition dependence of DNA helical conformation can be explained in terms of the opposing effects of thymine methyl groups of A · T base-pairs and the amino groups of G · C base-pairs upon the solvent within the grooves.The area calculations show that primarily the major groove of B-DNA and the minor groove of A-DNA have sufficient accessible surface area to be recognized by a probe size corresponding to the side-chains of amino acids.     

Differential behavior of cytotoxic effector cells against HLA antigens in strong genetic linkage disequilibrium

Five sets of cytotoxic effector cells were generated, using haploidentical, first degree relatives in five different families, against the HLA-A3; B7 serological determinants combined with different DR antigens. When tested against a panel of cells bearing combinations of the HLA-A, -B and -DR antigens it was shown that the HLA-B7 antigen was as strong a CML target determinant alone as it was in the presence of HLA-A3. The strength of the HLA-A3 antigen as target determinant varied. With effector cells primed to the HLA-A3; B7; DR2 haplotype, the A3 antigen alone behaved as a weak target determinant. When the same target cells were tested with the effector cells generated against HLA-A3; B7 without DR2, the A3 antigen behaved as a strong target determinant. A number of target cells lacking the serologically detectable HLA determinants present on the sensitizing HLA haplotype were identified as being killed by specific effector cells. These data suggest either a number of new CML target determinants controlled by different loci or the presence of a single, new locus with multiple alleles controlling CML targets.     

Protein production from whey usingPenicillium cyclopium; growth parameters and cellular composition

Summary The growth parameters ofPenicillium cyclopium have been evaluated in a continuous culture system for the production of fungal protein from whey. Dilution rates varied from 0.05 to 0.20 h^–1 under constant conditions of temperature (28°C) and pH (3.5). The saturation coefficients in the Monod equation were 0.74 g l^–1 for lactose and 0.14 mg l^–1 for oxygen, respectively. For a wide range of dilution rates, the yield was 0.68 g g^–1 biomass per lactose and the maintenance coefficient 0.005 g g^–1 h^–1 lactose per biomass, respectively. The maximum biomass productivity achieved was 2 g l^–1 h^–1 biomass at dilution rates of 0.16–0.17 h^–1 with a lactose concentration of 20 g l^–1 in the feed. The crude protein and total nucleic acid contents increased with a dilution rate, crude protein content varied from 43% to 54% and total nucleic acids from 6 to 9% in the range of dilution rates from 0.05 to 0.2 h^–1, while the Lowry protein content was almost constant at approximately 37.5% of dry matter.Nomenclature (mg l^–1) C_o initial concentration of dissolved oxygen - (h^–1) D dilution rate - (mg l^–1) K₀₂ saturation coefficient for oxygen - (g l^–1) K_s saturation coefficient for substrate - (g g^–1 h^–1) lactose per biomass) m maintenance energy coefficient - (mM g^–1 h^–1O₂ per biomass) Q₀₂ specific oxygen uptake rate - (g l^–1) S residual substrate concentration at steady state - (g l^–1) S_o initial substrate concentration in feed - (min) t_1/2 time when C_o is equal to C_o/2 - (g l^–1) X biomass concentration - (g l^–1) X biomass concentration at steady state - (g g^–1 biomass per lactose) Y_G yield coefficient for cell growth - (g g^–1 biomass per lactose) Y_x/s overall yield coefficient - (h^–1) specific growth rate     

Reduction by a model of NAD(P)H: XI. Stereochemistry of a lactate dehydrogenase-model reaction

Stereochemistry of the biomimetic reduction of α-keto esters with NAD(P)H-model compounds has been investigated. The model compound with the R-configuration reduces the α-keto esters to the (R)-α-hydroxy esters, whereas (S)-α-hydroxy esters are afforded by the reduction with the S-configurational model compounds. It has been concluded that pro-R and -S hydrogens of the model compounds with R- and S-configuration, respectively, contribute predominantly to the reduction.     

Role of adrenergic innervation in experimental renal hypertension

Renal hypertension was induced by ligation of the aorta between renal arteries in rats sympathectomized with 6-hydroxydopamine. In the early phase, equally severe hypertension developed in the denervated group as compared to innervated controls. Later, blood pressure was lower in the denervated rats. Initially, increases in plasma renin were seen in both groups; the levels, however, were markedly lower in the denervated rats. Later, the renin levels were similar and not different from baseline. It is concluded that adrenergic neural activity is not essential in the development of renal hypertension; the maintenance of the chronic state, however, depends in part on adrenergic innervation.     

Hemolytically active components from P. parvum and G. breve toxins

Hemolytically active fractions were isolated from the toxins produced by the red-tide dinoflagellate $\text{Gymnodinium breve}$ (GBTX) and the chrysomonad $\text{Prymnesium parvum}$ (PPTX). High pressure liquid chromatography through bonded phase (ODS) silica columns using a gradient of methanol in chloroform yielded 6 major fractions from GBTX, 3 of which were hemolytic (HD₅₀=0.3?0.56 μg·ml^?1). None were ichthyotoxic. Of the 6 fractions obtained from PPTX, 4 were hemolytic (HD₅₀=0.013?2.8 μg·ml^?1) but only one (fraction 6) was ichthyotoxic. This fraction was ～ 2000 times more hemolytic than the crude PPTX (HD₅₀=33.2 μg·ml^?1). Analysis of their UV spectra indicates that the fractions within each group are closely related.     

Crystal structure of yeast phenylalanine transfer RNA. II. Structural features and functional implications.

The structural features of yeast phenylalanine transfer RNA are analyzed and documented in detail, based on atomic co-ordinates obtained from an extensive crystallographic refinement of the crystal structure of the molecule at 2.7 Å resolution (see preceding paper). We describe here: the relative orientation and the helicity of the base-paired stems; more definitive assignments of tertiary hydrogen bonds involving bases, riboses and phosphates; binding sites for magnesium hydrates, spermine and water; iriter-molecular contacts and base-stacking; flexibility of the molecule; conformational analysis of nucleotides in the structure. Among the more noteworthy features are a considerable irregularity in the helicity of the base-paired stems, a greater flexibility in the anticodon and aminoacyl acceptor arms, and a “coupling” among several conformational angles. The functional implications of these structural features are also discussed.     

Electron microscopy of Mycoplasma pneumoniae microcolonies grown on solid surfaces.

Mycoplasma pneumoniae sprain CL-8 was studied by using various surfaces for adherence and growth. Cells grown on Epon 812, Formvar, carbon, and glass were of similar morphology. Thin Epon pieces were good material for culturing the organisms and examining thin-sectioned microcolonies by transmission electron microscopy.