To robotize chemistry laboratories. An example of organic synthesis: 2-Boc-amino-N-hydroxy-3-phenyl-propionamide.

The paper describes the development of periodic modules used for the peptide synthesis of hydroxamic acid. A powder conveyor using the principle of positive weighing distribution is described. Purification is provided using automatic filtration and a liquid- liquid extraction module separation device. Device quality is improved using failure mode and effects analysis.

Processing of beta-amyloid precursor protein by cathepsin D.

The events leading to the formation of beta-amyloid (betaA4) from its precursor (betaAPP) involve proteolytic cleavages that produce the amino and carboxyl termini of betaA4. The enzyme activities responsible for these cleavages have been termed beta- and gamma-secretase, respectively, although these protease(s) have not been identified. Since betaA4 is known to possess heterogeneity at both the amino and carboxyl termini, beta- and gamma-secretases may actually be a collection of proteolytic activities or perhaps a single proteolytic enzyme with broad amino acid specificity. We investigated the role of cathepsin D in the processing of betaAPP since this enzyme has been widely proposed as a gamma-secretase candidate. Treatment of a synthetic peptide that spans the gamma-secretase site of betaAPP with human cathepsin D resulted in the cleavage of this substrate at Ala42-Thr43. A sensitive liquid chromatography/mass spectrometry technique was also developed to further investigate the ability of cathepsin D to process longer recombinant betaAPP substrates (156 and 100 amino acids of betaAPP carboxyl terminus) in vitro. The precise cathepsin D cleavage sites within these recombinant betaAPP substrates were identified using this technique. Both recombinant substrates were cleaved at the following sites: Leu49-Val50, Asp68-Ala69, Phe93-Phe94. No cleavages were observed at putative gamma-secretase sites: Val40-Ile41 or Ala42-Thr43, suggesting that cathepsin D is not gamma-secretase as defined by these betaA4 termini. Under conditions where the betaAPP156 substrate was first denatured prior to cathepsin D digestion, two additional cleavage sites near the amino terminus of betaA4, Glu-3-Val-2 and Glu3-Phe4, were observed, indicating that cathepsin D cleavage of betaAPP is influenced by the structural integrity of the substrate. Taken together, these results indicate that in vitro, cathepsin D is unlikely to function as gamma-secretase; however, the ability of this enzyme to efficiently cleave betaAPP substrates at nonamyloidogenic sites within the molecule may reflect a role in betaAPP catabolism.

3-Amino-2-hydroxy-propionaldehyde and 3-amino-1-hydroxy-propan-2-one derivatives: new classes of aminopeptidase inhibitors.

3-Amino-2-hydroxy-propionaldehydes [H2NCH(R)CHOHCHO with R = H, i-Bu, CH2Ph] were designed as metallo-aminopeptidase inhibitors based on the metal active site chelation concept. These compounds were found to be micromolar inhibitors of aminopeptidase-M (AP-M, EC 3.4.11.2) with potencies similar to bestatin (Ki = 3.5 microM). Notably, compound 5a (R = H) is a selective inhibitor of AP-M (Ki = 7 microM) with respect to cytosolic leucine aminopeptidase (LAPc, EC 3.4.11.1) (Ki = 385 microM). However, due to their easy oligomerization, these compounds are low practical value. In contrast, the corresponding isomeric 3-amino-1-hydroxy-propan-2-one derivatives [H2NCH(R)COCH2OH with R = H, i-Bu, CH2Ph, i-Pr, CH2Biph] are well defined structures. These hydroxymethylketones also exhibit micromolar affinities on AP-M. Compound 6c (R = CH2Ph) was the most potent (Ki = 1 microM). Selectivity studies of 6a (R = H) and 6b (R=i-Bu) show a preference for AP-M. Compound 6a is moderately active on AP-M (Ki = 25 microM) and inactive on LAPc. This new class of inhibitors is proposed to bind as bidentates, analogous to hydroxamates.

The structure of the Aeromonas proteolytica aminopeptidase complexed with a hydroxamate inhibitor. Involvement in catalysis of Glu151 and two zinc ions of the co-catalytic unit.

The structure of the complex of Aeromonas proteolytica aminopeptidase, a two-zinc exopeptidase, with the inhibitor p-iodo-D-phenylalanine hydroxamate has been determined by X-ray crystallography. Refinement of the structure, which includes 220 water molecules, using data at 0.80-0.23-nm resolution resulted in a crystallographic residual R value of 16%. The hydroxamate group adopts a planar conformation whereby the two oxygen atoms interact with the zinc ions. The N-hydroxyl group of the inhibitor is located between the two zinc ions, a position which is close to that occupied by a water molecule in the native structure. The carbonyl oxygen of the inhibitor binds to Zn1, which becomes pentacoordinated while Zn2 remains tetracoordinated, in contrast to the native protein where both zinc ions were shown to be tetracoordinated and structurally equivalent. Interactions of the carboxylate oxygens of Glu151 with the hydroxamate group play an important role in the stabilization of the complex.

3-Amino-2-tetralone derivatives: novel potent and selective inhibitors of aminopeptidase-M (EC 3.4.11.2).

Derivatives of 3-amino-2-tetralone were evaluated for their ability to selectively inhibit the membrane-bound zinc-dependent aminopeptidase (EC 3.4.11.2), isolated from porcine kidney. These novel nonpeptidic compounds are potent competitive inhibitors of the enzyme. Some of them have Ki values in the nanomolar range (g, Ki = 80 nM). Moreover, these inhibitors are selective for aminopeptidase-M (AP-M) since they do not inhibit aspartate aminopeptidase and arginine aminopeptidase and only poorly inhibit cytosolic leucine aminopeptidase at high concentrations (g, Ki = 70 microM). The availability of inhibitors which are selective for AP-M with respect to other mammalian aminopeptidases may aid in identifying new endogenous substrates and thus clarify the physiological or pathophysiological role(s) of AP-M.

Crystal structure of Aeromonas proteolytica aminopeptidase: a prototypical member of the co-catalytic zinc enzyme family.

BACKGROUND: Aminopeptidases specifically cleave the amino-terminal residue from polypeptide chains and are involved in the metabolism of biologically active peptides. The family includes zinc-dependent enzymes possessing either one or two zinc ions per active site. Structural studies providing a detailed view of the metal environment may reveal whether the one-zinc and two-zinc enzymes constitute structurally and mechanistically distinct subclasses, and what role the metal ions play in the catalytic process. RESULTS: We have solved the crystal structure of the monomeric aminopeptidase from Aeromonas proteolytica at 1.8 A resolution. The protein is folded into a single alpha/beta globular domain. The active site contains two zinc ions (3.5 A apart) with shared ligands and symmetrical coordination spheres. We have compared it with the related bovine lens leucine aminopeptidase and the cobalt-containing Escherichia coli methionine aminopeptidase. CONCLUSIONS: The environment and coordination of the two zinc ions in A. proteolytica aminopeptidase strongly support the view that the two metal ions constitute a co-catalytic unit and play equivalent roles during catalysis. This conflicts with the conclusions drawn from the related bovine leucine aminopeptidase and early biochemical studies. In addition, the known specificity of the aminopeptidase for hydrophobic amino-terminal residues is reflected in the hydrophobicity of the active site cleft.

Structure activity relationship of phosphoramidon derivatives for in vivo endothelin-converting-enzyme inhibition.

The structure activity relationship of phosphoramidon analogues was studied for their ability to reduce the hypertensive effect of exogenous proET-1, probably via inhibition of an endothelin converting enzyme activity (ECE). Results concerning in vivo ECE and in vitro thermolysin inhibitions were compared. In contrast to the phosphoryl group of phosphoramidon, which was found to be an absolute requirement, the rhamnose moiety was of very little importance for the inhibition of either enzyme. Furthermore, the tryptophan residue of phosphoramidon appeared to be particularly important for the ECE inhibition, whereas thermolysin inhibition seemed to depend greatly on the leucine residue. It is concluded that in vivo ECE and thermolysin differ in the way they recognise phosphoramidon. The existence of an hydrophobic pocket, specific for the recognition of the tryptophan residue of phosphoramidon, could be proposed for ECE.

Mechanism of the inhibition of cholesterol biosynthesis by 6-fluoromevalonate.

6-Fluoromevalonate blocks the incorporation of mevalonic acid, but not that of isopentenyl pyrophosphate, into non-saponifiable lipids in a rat liver multienzyme system. With 3H-labelled 6-fluoromevalonate, it was found that 6-fluoromevalonate is converted to its phospho and pyrophospho derivatives in this system. The kinetics of the two kinases were studied. 6-Fluoromevalonate 5-pyrophosphate is a potent competitive inhibitor of pyrophosphomevalonate decarboxylase (Ki 37 nM). In the multienzyme assay for cholesterol biosynthesis, there is accumulation of mevalonate 5-phosphate and mevalonate 5-pyrophosphate in the presence of 5 microM-6-fluoromevalonate, and 6-fluoromevalonate 5-pyrophosphate is more effective than 6-fluoromevalonate in inhibiting cholesterol biosynthesis. We suggest therefore that 6-fluoromevalonate blocks cholesterol biosynthesis at the level of pyrophosphomevalonate decarboxylase after being pyrophosphorylated.