Oxygen activation occurs at a wide variety of enzyme active sites. Mechanisms previously proposed for the copper monooxygenase, dopamine ␤-monooxygenase (D␤M), involve the accumulation of an activated oxygen intermediate with the properties of a copper-peroxo or copper-oxo species before substrate activation. These are reminiscent of the mechanism of cytochrome P-450, where a heme iron stabilizes the activated O 2 species. Herein, we report two experimental probes of the activated oxygen species in D␤M. First, we have synthesized the substrate analog, ␤,␤-difluorophenethylamine, and examined its capacity to induce reoxidation of the prereduced copper sites of D␤M upon mixing with O 2 under rapid freeze-quench conditions. This experiment fails to give rise to an EPR-detectable copper species, in contrast to a substrate with a C-H active bond. This indicates either that the reoxidation of the enzyme-bound copper sites in the presence of O 2 is tightly linked to C-H activation or that a diamagnetic species Cu(II)-O 2 ⅐ ⅐ has been formed. In the context of the open and fully solvent-accessible active site for the homologous peptidylglycine-␣-hydroxylating monooxygenase and by analogy to cytochrome P-450, the accumulation of a reduced and activated oxygen species in D␤M before C-H cleavage would be expected to give some uncoupling of oxygen and substrate consumption. We have, therefore, examined the degree to which O 2 and substrate consumption are coupled in D␤M using both end point and initial rate experimental protocols. With substrates that differ by more than three orders of magnitude in rate, we fail to detect any uncoupling of O 2 uptake from product formation. We conclude that there is no accumulation of an activated form of O 2 before C-H abstraction in the D␤M and peptidylglycine-␣-hydroxylating monooxygenase class of copper monooxygenases, presenting a mechanism in which a diamagnetic Cu(II)-superoxo complex, formed initially at very low levels, abstracts a hydrogen atom from substrate to generate Cu(II)-hydroperoxo and substrate-free radical as intermediates. Subsequent participation of the second copper site per subunit completes the reaction cycle, generating hydroxylated product and water. Dopamine ␤-monooxygenase (D␤M) 1 along with peptidylglycine-␣-hydroxylating monooxygenase (PHM) comprise a unique class of enzymes that contain only copper as a cofactor and catalyze the cleavage of O 2 to form hydroxylated product and water. D␤M is of central importance in the catecholamine biosynthetic pathway, catalyzing the conversion of dopamine to norepinephrine (Scheme 1, top), where both substrate and product serve as neurotransmitters within the central nervous system (1). Primarily localized within the secretory granules of adrenal chromaffin cells and neurons, D␤M is a large, tetrameric glycoprotein (75 kDa per monomer) consisting of two disulfide-linked dimers.Although no crystal structure has been reported, extensive structural data exist for D␤M. Extended X-ray absorption fine structure was used to char...

Fatty acid amide hydrolase (FAAH) is an integral membrane enzyme that degrades the fatty acid amide family of signaling lipids, including the endocannabinoid anandamide. Genetic or pharmacological inactivation of FAAH leads to analgesic, anti-inflammatory, anxiolytic, and antidepressant phenotypes in rodents without showing the undesirable side effects observed with direct cannabinoid receptor agonists, indicating that FAAH may represent an attractive therapeutic target for treatment of pain, inflammation, and other central nervous system disorders. However, the FAAH inhibitors reported to date lack druglike pharmacokinetic properties and/or selectivity. Herein we describe piperidine/piperazine ureas represented by and N-phenyl-4-(quinolin-2-ylmethyl)piperazine-1-carboxamide (PF-622) as a novel mechanistic class of FAAH inhibitors. PF-750 and PF-622 show higher in vitro potencies than previously established classes of FAAH inhibitors. Rather unexpectedly based on the high chemical stability of the urea functional group, PF-750 and PF-622 were found to inhibit FAAH in a time-dependent manner by covalently modifying the enzyme's active site serine nucleophile. Activity-based proteomic profiling revealed that PF-750 and PF-622 were completely selective for FAAH relative to other mammalian serine hydrolases. We hypothesize that this remarkable specificity derives, at least in part, from FAAH's special ability to function as a C(O)-N bond hydrolase, which distinguishes it from the vast majority of metabolic serine hydrolases in mammals that are restricted to hydrolyzing esters and/or thioesters. The piperidine/piperazine urea may thus represent a privileged chemical scaffold for the synthesis of FAAH inhibitors that display an unprecedented combination of potency and selectivity for use as potential analgesic and anxiolytic/antidepressant agents.Fatty acid amide hydrolase (FAAH 1 ) is an integral membrane enzyme (1, 2) that regulates the fatty acid amide family of lipid transmitters, which includes the endogenous cannabinoid N-arachidonyl ethanolamine (anandamide) (3), the anti-inflammatory factor N-palmitoyl ethanolamine (PEA) (4), the sleep-inducing substance 9(Z)-octadecenamide (oleamide) (5), and the satiating signal N-oleoyl ethanolamine (OEA) (6).FAAH inactivation by either genetic deletion of the FAAH gene in mice (7) or by chemical inhibitors (8) leads to elevated endogenous levels of fatty acid amides with concomitant analgesic (9-13), anxiolytic (8), antidepressant (14, 15), sleep-enhancing (16), and anti-inflammatory (9,17,18) phenotypes. Notably the behavioral phenotypes observed in FAAH knockout (-/-) mice (7, 9) or in rodents treated with FAAH inhibitors (8,(11)(12)(13)(14)18) occur in the absence of alterations in motility, weight gain, or body temperature that are typically observed with direct cannabinoid receptor 1 (CB1) agonists. These findings suggest that FAAH may represent an attractive therapeutic target for treatment of pain, inflammation, and other central nervous system (CNS) diso...

Although FAAH suppression can elicit significant effects under some instances in which consequential procedural modifications are made, the present results indicate that the pharmacological inhibition or genetic deletion of FAAH is ineffective in standard mouse models of emotional reactivity. It remains to be established whether the effects of FAAH inhibition in these modified tasks are predictive of their efficacy in treating emotional disorders.

Endothelins are peptide hormones with a potent vasoconstrictor activity that are also known to function as intercellular signaling molecules. The final step in the biosynthesis of endothelins is the proteolytic processing of precursor peptides by endothelin-converting enzymes (ECEs). ECE-1 is a zinc metalloendopeptidase related in amino acid sequence to neprilysin, a mammalian cell-surface peptidase involved in the metabolism of numerous biologically active peptides. Despite apparent structural similarities, ECE-1 and neprilysin have been considered to differ significantly in substrate specificity. In this study we have examined the activity of recombinant ECE-1 against a collection of biologically active peptides. ECE-1, unlike neprilysin, was found to have minimal activity against substrates smaller than hexapeptides, such as Leu-enkephalin. Larger peptides such as neurotensin, substance P, bradykinin, and the oxidized insulin B chain were hydrolyzed by ECE-1 as efficiently as big endothelin-1, a known in vivo substrate. Identification of the products of hydrolysis of six peptides indicates that ECE-1 has a substrate specificity similar to that of neprilysin, preferring to cleave substrates at the amino side of hydrophobic residues. The data indicate that ECE-1 possesses a surprisingly broad substrate specificity and is potentially involved in the metabolism of biologically active peptides distinct from the endothelins. Endothelins (ETs)1 are potent vasoconstrictive peptides of 21 amino acids produced by vascular endothelial cells (1). Three ET isoforms, ET-1, ET-2, and ET-3, encoded by distinct genes, are known to exist in humans (2). Endothelins are involved in the regulation of vascular tone and may also play roles in various cardiovascular and renal diseases (3). ETs are also required during embryonic development for the intercellular signaling necessary for the proper development of neural crestderived tissues (4). The final step in the biosynthesis of the endothelins is the conversion of 38 -41 residue precursors (big ETs) to the active hormones via the cleavage of a Trp 21 -Val/ Ile 22 bond by endothelin-converting enzymes (ECEs (5)). ECE-1 has been purified from vascular endothelium, endothelial cell lines, and lung microsomes (6 -8). ) is a Type II integral membrane protein expressed by endothelial cells in tissues such as aorta, lung, ovary, and testis. It has also been reported to be expressed by endocrine cells such as adrenal chromaffin cells and pancreatic ␤ cells (9). Targeted disruption of the ECE-1 gene has shown that ECE-1 is the physiologically relevant activating enzyme for both ET-1 and ET-3 in vivo (10).Molecular cloning of mammalian ECE-1 cDNAs has demonstrated the existence of three mRNAs transcribed from a single gene (11,12). The proteins encoded by these RNAs have identical catalytic domains but differ only in their NH 2 -terminal amino acid sequence. Two of the ECE-1 isoforms are expressed on the cell surface; the other is localized in the trans-Golgi network (12) An additional isof...