Saccharomyces cerevisiae has a single glutamate synthase gene coding for a plant-like high-molecular-weight polypeptide.

Purification of the glutamate synthase (GOGAT) enzyme from Saccharomyces cerevisiae showed that it is an oligomeric enzyme composed of three identical 199-kDa subunits. The GOGAT structural gene was isolated by screening a yeast genomic library with a yeast PCR probe. This probe was obtained by amplification with degenerate oligonucleotides designed from conserved regions of known GOGAT genes. The derived amino-terminal sequence of the GOGAT gene was confirmed by direct amino-terminal sequence analysis of the purified protein of 199 kDa. Northern (RNA) analysis allowed the identification of an mRNA of about 7 or 8 kb. An internal fragment of the GOGAT gene was used to obtain null GOGAT mutants completely devoid of GOGAT activity. The results show that S. cerevisiae has a single NADH-GOGAT enzyme, consisting of three 199-kDa monomers, that differs from the one found in prokaryotic microorganisms but is similar to those found in other eukaryotic organisms such as alfalfa.     

E-2078, a potent, selective and stable dynorphin analog with preferential activity for the kappa-opioid receptor subtype on the mouse vas deferens neuroeffector junction

The profile of opioid activity of E-2078, a synthetic stable dynorphin analog, was examined in the mouse vas deferens bioassay and compared to that of methionine enkephalin and nonpeptide kappa agonists in the absence and in the presence of selective antagonists for the mu-, kappa- and delta-opioid receptor subtypes. The inhibitory action of E-2078 and related kappa agonists was specifically and potently antagonized only by norbinaltorphimine, revealing the presence of kappa receptors in this tissue and the predominant kappa activity of E-2078.     

Facile preparation of disulfide-bridged peptides using the polymer-supported oxidant CLEAR-OX.

Formation of disulfide bonds in synthetic peptides is one of the more challenging transformations to achieve in peptide chemistry, in view of the possible formation of oligomeric by-products and other side reactions, as well as occasional solubility problems in aqueous oxidizing media. It was shown previously that 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB identical with Ellman's reagent), when attached to polyethylene glycol-polystyrene (PEG-PS), controlled-pore glass (CPG), or modified Sephadex supports, was an effective oxidizing agent that promoted disulfide formation under mild conditions. More recently, this work was extended to Cross-Linked Ethoxylate Acrylate Resin (CLEAR) supports, because of their compatibility with both organic and aqueous solvent mixtures. The resultant new tool, termed CLEAR-OX, was used to conveniently produce several model cyclic disulfides with improved purities and yields, when compared with solution oxidations. A particularly striking example was the gram-scale oxidation of a urotensin II antagonist peptide containing a hindered penicillamine unit.     

The biological significance of malondialdehyde determination in the assessment of tissue oxidative stress

Although lipid peroxidation of biological samples may be assessed by different chemical and physical methods, those based on the measurement of malondialdehyde formed from the breakdown of endoperoxides during the last stages of the oxidation of a polyunsaturated fatty acid, appear as the most widely used. Among the various methods to evaluate malondialdehyde, which include direct spectrophotometry or high pressure liquid chromatography, the reaction with thiobarbituric acid to form a colored adduct appears as a more rapid, inexpensive and sensitive technique. This method, however, is subject to some interferences which, if not considered, may lead to erroneous results. The present review emphasizes the significance of malondialdehyde measurement in biological samples, the chemical conditions of its reaction with thiobarbituric acid and the different procedures to isolate and determine the malondialdehyde-thiobarbituric acid adduct.