The aminocoumarin antibiotic coumermycin A1 produced by Streptomyces rishiriensis DSM 40489 contains two amide bonds. The biosynthetic gene cluster of coumermycin contains a putative amide synthetase gene, couL , encoding a protein of 529 amino acids. CouL was overexpressed as hexahistidine fusion protein in Escherichia coli and purified by metal affinity chromatography, resulting in a nearly homogenous protein. CouL catalysed the formation of both amide bonds of coumermycin A1, i.e. between the central 3‐methylpyrrole‐2,4‐dicarboxylic acid and two aminocoumarin moieties. Gel exclusion chromatography showed that the enzyme is active as a monomer. The activity was strictly dependent on the presence of ATP and Mn2+ or Mg2+. The apparent K m values were determined as 26 µm for the 3‐methylpyrrole‐2,4‐dicarboxylic acid and 44 µm for the aminocoumarin moiety, respectively. Several analogues of the pyrrole dicarboxylic acid were accepted as substrates. In contrast, pyridine carboxylic acids were not accepted. 3‐Dimethylallyl‐4‐hydroxybenzoic acid, the acyl component in novobiocin biosynthesis, was well accepted, despite its structural difference from the genuine acyl substrate of CouL.

Dipeptidyl peptidase IV (DP IV, CD26) plays an essential role in the activation and proliferation of lymphocytes, which is shown by the immunosuppressive effects of synthetic DP IV inhibitors. Similarly, both human immunodeficiency virus‐1 (HIV‐1) Tat protein and the N‐terminal peptide Tat(1–9) inhibit DP IV activity and T cell proliferation. Therefore, the N‐terminal amino acid sequence of HIV‐1 Tat is important for the inhibition of DP IV. Recently, we characterized the thromboxane A2 receptor peptide TXA2‐R(1–9), bearing the N‐terminal MWP sequence motif, as a potent DP IV inhibitor possibly playing a functional role during antigen presentation by inhibiting T cell‐expressed DP IV [Wrenger, S., Faust, J., Mrestani‐Klaus, C., Fengler, A., Stöckel‐Maschek, A., Lorey, S., Kähne, T., Brandt, W., Neubert, K., Ansorge, S. & Reinhold, D. (2000) J. Biol. Chem. 275 , 22180–22186]. Here, we demonstrate that amino acid substitutions at different positions of Tat(1–9) can result in a change of the inhibition type. Certain Tat(1–9)‐related peptides are found to be competitive, and others linear mixed‐type or parabolic mixed‐type inhibitors indicating different inhibitor binding sites on DP IV, at the active site and out of the active site. The parabolic mixed‐type mechanism, attributed to both non‐mutually exclusive inhibitor binding sites of the enzyme, is described in detail. From the kinetic investigations and molecular modeling experiments, possible interactions of the oligopeptides with specified amino acids of DP IV are suggested. These findings give new insights for the development of more potent and specific peptide‐based DP IV inhibitors. Such inhibitors could be useful for the treatment of autoimmune and inflammatory diseases.

An abundant catalytically active β‐amylase (EC 3.2.1.2) was isolated from resting rhizomes of hedge bindweed (Calystegia sepium ). Biochemical analysis of the purified protein, molecular modeling, and cloning of the corresponding gene indicated that this enzyme resembles previously characterized plant β‐amylases with regard to its amino‐acid sequence, molecular structure and catalytic activities. Immunolocalization demonstrated that the β‐amylase is exclusively located in the cytoplasm. It is suggested that the hedge bindweed rhizome β‐amylase is a cytoplasmic vegetative storage protein.

The formation of phytochelatins, small metal‐binding glutathione‐derived peptides, is one of the well‐studied responses of plants to toxic metal exposure. Phytochelatins have also been detected in some fungi and some marine diatoms. Genes encoding phytochelatin synthases (PCS) have recently been cloned from Arabidopsis , wheat and Schizosaccharomyces pombe . Surprisingly, database searches revealed the presence of a homologous gene in the Caenorhabditis elegans genome, DDBJ/EMBL/GenBank accession no. 266513. Here we show that C. elegans indeed expresses a gene coding for a functional phytochelatin synthase. CePCS complements the Cd2+ sensitivity of a Schizosaccharomyces pombe PCS knock‐out strain and confers phytochelatin synthase activity to these cells. Thus, phytochelatins may play a role for metal homeostasis also in certain animals.

A model of the binding site of δ‐opioids in the extracellular region of the G‐protein‐coupled opioid receptor based on modelling studies is presented. The distance between Asp288 and the disulfide bridge (Cys121–Cys198) formed between the first and second extracellular loops was found to be short. This model is consistent with site‐directed mutagenesis studies. The arrangement of the ligands found in the receptor led to the development of a reaction mechanism for the cleavage of the disulfide bond catalysed by the ligands. Semi‐empirical quantum chemical PM3 and AM1 calculations as well as ab initio studies showed that the interaction between the carboxylic acid side chain of aspartic acid and the disulfide bond leads to the polarization of, and withdrawal of a proton from, the protonated nitrogen of the ligand to one of the sulfur atoms. A mixed sulfenic acid and carboxylic acid anhydrate is formed as an intermediate as well as a thiol. The accompanying cleavage of the disulfide bond may produce a conformational change in the extracellular loops such that the pore formed by the seven‐helix bundle opens allowing entrance of the ligand, water and ions into the cell. Cleavage of the disulfide bond after opioid administration was demonstrated experimentally by flow‐cytometric measurements employing CMTMR and monobromobimane‐based analyses of membrane‐located thiols. The suggested mechanism may explain, in a consistent way, the action of agonists and antagonists and is assumed to be common for many G‐protein coupled receptors.

We found three methyl jasmonate−induced lipoxygenases with molecular masses of 92 kDa, 98 kDa, and 100 kDa (LOX‐92, ‐98 and ‐100) [Feussner, I., Hause, B., Vörös, K., Parthier, B. & Wasternack, C. (1995) Plant J. 7 , 949−957]. At least two of them (LOX‐92 and LOX‐100), were shown to be localized within chloroplasts of barley leaves. Here, we describe the isolation of a cDNA (3073 bp) coding for LOX‐100, a protein of 936 amino acid residues and a molecular mass of 106 kDa. By sequence comparison this lipoxygenase could be identified as LOX2‐type lipoxygenase and was therefore designated LOX2 : Hv : 1 . The recombinant lipoxygenase was expressed in Escherichia coli and characterized as linoleate 13‐LOX and arachidonate 15‐LOX, respectively. The enzyme exhibited a pH optimum around pH 7.0 and a moderate substrate preference for linoleic acid. The gene was transiently expressed after exogenous application of jasmonic acid methyl ester with a maximum between 12 h and 18 h. Its expression was not affected by exogenous application of abscisic acid. Also a rise of endogenous jasmonic acid resulting from sorbitol stress did not induce LOX2 : Hv : 1 , suggesting a separate signalling pathway compared with other jasmonate‐induced proteins of barley. The properties of LOX2 : Hv : 1 are discussed in relation to its possible involvement in jasmonic acid biosynthesis and other LOX forms of barley identified so far.