A Search for the Intermediate Radical, ONOO', in the Reaction Between Oxygen and Nitric Oxide in Solution

The most probable initial reaction between NO and O₂ is direct addition to give the peroxyl radical ONOO. In view of the potential importance of this radical in biology, we have searched extensively for its formation, using EPR spectroscopy and rapid freezing techniques. At best, only extremely low concentrations were detected, and in most systems, no signals were detectable. We conclude that this radical is unlikely to be of major importance per se in biological systems, in contrast with its one electron adduct, the peroxynitrite anion.     

Structure and order of the protein and carbohydrate domains of prothrombin fragment 1

The three-dimensional structure of prothrombin fragment 1 has been determined by X-ray crystallography at 3.8 A resolution. The fragment is composed of a number of structural units, some of which are ordered while others are disordered. The ordered part of the structure includes a compact kringle unit, a helical domain and a carbohydrate chain. The kringle structure is organized around a close pair of buried disulfide bridges. One of its carbohydrate chains, that attached to Asn 101, is fully ordered, but the carbohydrate chain attached to Asn 77 appears to be disordered. The calcium binding unit is composed of a disordered part containing all ten gamma-carboxyglutamic acid residues and an ordered part forming the helical domain. The highly conserved residues Phe 41, Trp 42 and Tyr 45, which form a hydrophobic cluster on the first helix, interact around a crystallographic two-fold axis with the equivalent residues in another molecule to form a dimer in the crystal.     

Chromatin decondensation and DNA synthesis in human sperm activated in vitro by using Xenopus laevis egg extracts

An in vitro sperm activation system was used to study nuclear swelling-chromatin decondensation and DNA synthesis; processes that occur in vivo following fertilization. Lysolecithin-permeabilized human sperm were incubated in Xenopus laevis egg extract and examined by using phase-contrast light microscopy, electron microscopy, and autoradiography. During a 3-hour incubation, the activated sperm nuclear chromatin underwent a decondensation-recondensation cycle during which DNA was synthesized. This also occurred when egg extract was given a 3-hour preincubation before the addition of the sperm, suggesting that the factor(s) required for initiating the decondensation-recondensation cycle is associated with the sperm. Because both nuclear swelling and DNA synthesis were found to be reproducible and quantifiable, we studied the effect of various agents on the two processes, characterizing the critical component(s) in the egg extract that induces these events. EGTA was found to have no effect on the induced nuclear swelling or DNA synthesis that occurs in the activated sperm. Freezing and thawing the extract or treating the extract with aphidicolin also had no effect on subsequent nuclear swelling; however, the DNA synthesis activity was blocked. Sperm incubated in extract treated with alkaline phosphatase (AP) had both nuclear swelling and DNA synthesis blocked. However, if the sperm were pretreated with DTT, and then incubated with the AP-treated extract, only the DNA synthesis activity of the extract was blocked. When the extract was treated with serine protease inhibitors (PMSF, soybean trypsin inhibitor, or alpha-2-macroglobulin), nuclear swelling occurred; however, DNA synthesis was blocked. These data suggest that phosphoproteins are involved in one or more of the activation events and that a serine protease(s) is involved in the synthesis of DNA.     

Bioengineering nisin to overcome the nisin resistance protein

The emergence and dissemination of antibiotic resistant bacteria is a major medical challenge. Lantibiotics are highly modified bacterially produced antimicrobial peptides that have attracted considerable interest as alternatives or adjuncts to existing antibiotics. Nisin, the most widely studied and commercially exploited lantibiotic, exhibits high efficacy against many pathogens. However, some clinically relevant bacteria express highly specific membrane‐associated nisin resistance proteins. One notable example is the nisin resistance protein that acts by cleaving the peptide bond between ring E and the adjacent serine 29, resulting in a truncated peptide with significantly less activity. We utilised a complete bank of bioengineered nisin (nisin A) producers in which the serine 29 residue has been replaced with every alternative amino acid. The nisin A S29P derivative was found to be as active as nisin A against a variety of bacterial targets but, crucially, exhibited a 20‐fold increase in specific activity against a strain expressing the nisin resistance protein. Another derivative, nisin PV, exhibited similar properties but was much less prone to oxidation. This version of nisin with enhanced resistance to specific resistance mechanisms could prove useful in the fight against antibiotic resistant pathogens.     

Bioalkylation of dibenz[a,b]anthracene in rat liver cytosol

Previous studies by other investigators have established that L-region methyl derivatives of dibenz[a,h]anthracene (DBA) were more carcinogenic than the parent hydrocarbon. The bioalkylation of DBA was investigated by incubating the hydrocarbon with rat liver cytosol fortified with S-adenosyl-L-methionine (SAM) in 0.1 M phosphate buffer (pH 7.4) for 1 h at 37 degrees C in air. The reaction was stopped by the addition of cold acetone and the mixture extracted with ethyl acetate and washed with water. The organic phase was evaporated and the residue dissolved in methylene chloride for analysis by reverse phase high performance liquid chromatography (HPLC) and gas chromatography/mass spectroscopy GC/MS. Products were found that were indistinguishable from 7-methyl-DBA and 7,14-dimethyl-DBA, 7-hydroxymethyl-DBA, 7-hydroxymethyl-14-methyl-DBA, and 7,14-dihydroxymethyl-DBA. The results suggest that unsubstituted carcinogenic hydrocarbons are preprocarcinogens that react with SAM in liver cytosol preparations, to form alkyl substituted procarcinogens, which are more potent than the corresponding preprocarcinogens.