Halogen chemistry of the red alga Bonnemaisonia

Complete accounts of the natural products chemistry of Bonnemaisonia nootkana, B. asparagoides, B. hamifera and Trailliella intricata are described. In contrast to the chemistry of the closely related alga Asparagopsis, Bonnemaisonia spp. do not produce halomethanes, but instead an array of C₇-C₉ halogen-containing ketones, alcohols and carboxylic acids. Biomimetic syntheses of these compounds suggest they are precursors and products of in vivo Favorsky rearrangements.     

Phase Equilibria in binary mixtures of dimyristoylphosphatidylcholine and cardiolipin

Paramagnetic resonance spectra of the spin-label 2,2,6,6-tetramethylpiperidinyl-l-oxy have been used to study phase separations in binary mixtures of dimyristoyl-phosphatidylcholine and cardiolipin. Two different samples of cardiolipin were used: (i) One sample contained calcium ions at a mole ratio of calcium:cardiolipin = 1:2; the experimental data support the view that cardiolipin is present in the bilayer membrane as calcium ion linked dimers, (CL)2 Ca2+. (ii) A calcium-free sodium cardiolipin sample yielded remarkable spin-label partition data that were quite different from those obtained in the presence of Ca2+. In both cases the spin-label data provide evidence for compound formation and for fluid-fluid immiscibility in the bilayer membrane.     

Plasmids coding for heat-labile enterotoxin production isolated from Escherichia coli O78: comparison of properties.

Nineteen enterotoxigenic Escherichia coli strains of serogroup O78, isolated in different geographical areas from humans with diarrheal diseases, were tested for their ability to transfer enterotoxin production. All of the strains originally produced heat-labile enterotoxin, and 16 also produced heat-stable enterotoxin and colonization factor antigen I. Plasmids coding for the production of heat-labile enterotoxin only were transferred from 13 strains. Some properties of these plasmids were compared. All were fi+, but they could be divided into three groups on the basis of their incompatibility reactions, ability to restrict E. coli K-12 phages, and size. The three heat-labile enterotoxin plasmids isolated from African strains all belonged to one enterotoxin plasmid group. The heat-labile enterotoxin plasmids from the Asian strains were divided into two groups, those from serotype O78.H11 differing from those from serotype O78.H12.     

Application of pattern recognition and feature extraction techniques to volatile constituent metabolic profiles obtained by capillary gas chromatography

The applicability of threshold logic units, a form of nonparametric pattern recognition, to the processing of metabolic profile data obtained by high-efficiency glass capillary column gas chromatography has been investigated. The test data included profiles of the volatile constituents of urine from normal individuals and from individuals with diabetes mellitus. A feature extraction algorithm allowed for dimensionality reduction and indicated the constituents most important in the normal versus pathological distinction. With an optimum number of dimensions, a normal versus pathological prediction rate of 93.75% was achieved. Gas chromatography—mass spectrometry was utilized to identify important profile constituents.     

Exchange mechanisms for hydrogen bonding protons of cytidylic and guanylic acids.

The pH dependence of buffer catalysis of exchange of the C-4 amino protons of cyclic cytosine 2',3'-monophosphate (cCMP) and the N-1 proton of cyclic guanosine 2',3'-monophosphate (cGMP) conforms to an exchange mechanism, in which protonation of the nucleobases at C(N-3) AND G(N-7) establishes the important intermediates at neutral to acidic pH. Rate constants for transfer of the G(N-1) proton to H2O, OH-, phosphate, acetate, chloracetate, lactate, and cytosine (N-3) were obtained from 1H nuclear magnetic resonance line width measurements at 360 MHz and were used to estimate the pK or acidity of the exchange site in both the protonated and unprotonated nucleobase. These estimates reveal an increase in acidity of the G(N-1) site corresponding to 2 to 3 pK units as the G(N-7) site is protonated: At neutral pH the G(N-1) site of the protonated purine would be ionized (pK = 6.3). Determinations of phosphate, imidazole, and methylimidazole rate constants for transfer of the amino protons of cCMP provide a more approximate estimate of pK = 7 to 9 for the amino of the protonated pyrimidine. A comparison of the intrinsic amino acidity in the neutral and protonated cytosine is vitiated by the observation that OH- catalyzed exchange in the neutral base is not diffusion limited. This leads to the conclusion that protonation of the nucleobase effects a qualitative increase in the ability of the amino protons to form hydrogen bonds: from very poor in the neutral base to "normal" in the conjugate acid.     

Surface areas of lipid membranes

Upon photolysis, alkyl pentacyanocobaltate complexes generate alkyl radicals which react rapidly and specifically with nitroxide radicals, and which do not penetrate phospholipid bilayers. By measuring the loss of paramagnetic resonance signal intensity when multilamellar liposomes containing a small amount of spin-labeled lipid are exposed to these radicals, we have measured the proportion of lipid on the external surface of liposomes. We have shown that liposomes prepared under specified conditions from dimyristoylphosphatidylcholine, dipalmitoylphosphatidylcholine, and binary mixtures of dipalmitoylphosphatidylcholine and cholesterol all have the same proportion of external lipid.     

Interactions of proteins and cholesterol with lipids in bilayer membranes.

Mixtures of lipids and protein, the ATPase from rabbit sarcoplasmic reticulum, were studied by freeze-fracture electron microscopy and by measurement of the amount of fluid lipid with the spin label 2,2,6,6-tetramethylpiperidine-1-oxyl (TEM-PO). In dimyristoyl phosphatidylcholine vesicles the protein molecules were randomly distributed above the transition temperature, Tt, of the lipid and aggregated below Tt. For mixtures of dimyristoyl and dipalmitoyl phosphatidylcholine the existence of fluid and solid domains were shown in the temperature interval predicted from earlier TEMPO measurements. When protein was incorporated into this lipid mixture, freeze-fracture particles were randomly distributed in fluid lipids, or aggregated when only solid lipids were present. In mixtures of dimyristoyl phosphatidylcholine with cholesterol the protein was distributed randomly above the transition temperature of the phosphatidylcholine. Below that transition temperature the protein was excluded from a banded phase of solid lipid in the case of 10 mol% cholesterol. In mixtures containing 20 mol% cholesterol, protein molecules formed linear arrays, 50-200 nm in length, around smooth patches of lipid. Phase diagrams for lipid/cholesterol and lipid/protein systems are proposed which account for many of the available data. A model for increasing solidification of lipid around protein molecules or cholesterol above the transition temperature of the lipid is discussed.     

Activation of the alternative complement pathway by lymphoblastoid cell lines derived from patients with Burkitt's lymphoma and infectious mononucleosis.

Cultured human lymphoblastoid cell lines derived from patients with Burkitt's lymphoma or infectious mononucleosis were shown to activate the alternative pathway of complement fixation. This reaction does not require any conventional antibody directed against the cells. Although the reaction showed an absolute dependence on the presence of factor B it was relatively independent of the presence of factor D or of properdin. To this extent activation of the alternative pathway by lymphoblastoid cells resembles that produced by “C3-nephritic factor.” Rat and mouse complement were activated in a manner similar to human complement, but guinea pig complement was inactive. Chicken complement, unlike any of the mammalian complements tested, was able to bring about lysis of the lymphoblastoid cell lines by the alternative pathway.