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Kinetic studies of carboxypeptidase Y. III. Action on ester, amide, and anilide substrates and the effects of some environmental factors.

Kinetic parameters of carboxypeptidase Y are given for the hydrolyses of ester, amide, and anilide substrates. The kcat/Km values were compatible with those of chymotrypsin [EC 3.4.21.1] with a few exceptions. One ionizable group with a pK of around 5.8 was suggested to be involved in the free enzyme in hydrolyzing all the substrates, including peptide substrates. In addition, hydroxylaminolysis and the kinetic isotope effects of deuterium oxide indicated, with some reservations, a reaction mechanism which proceeds via the formation of an acyl intermediate.

Amides

Spasmolytic activity of two synthetic anilide local anaesthetics.

Two basic anilides EA-7 and EA-8 were investigated for their antispasmodic activity against a variety of spasmogens on different tissues from different species of animals and comparison was made with lignocaine. EA-8 was found to be the most potent in this respect, followed by EA-7 and lignocaine. The antispasmodic potency does not correspond to their local anaesthetic potency. This suggests a direct depressant effect on tissues.

Acetylcholine

Further studies of metyrapone effects upon anilide hydroxylation.

The enhancing effect of metyrapone upon the p-hydroxylation of acetanilide has been confirmed with the use of a new gas-chromatographic method for the determination of acetaminophen. This effect has been shown not to be due to inhibition of hydrolysis of acetaminophen or interference with its determination, or to preferential formation of other phenolic metabolites. This effect of metyrapone is remarkably substrate-specific: phenol formation from the homologues of acetanilide, formanilide and propionanilide, and that from the sulfonamide analog of acetanilide, methanesulfonanilide, is inhibited by metyrapone over the concentration range in which acetanilide hydroxylation is enhanced. The same substrate specificity was observed when the modifier was acetophenone. alpha,alpha'-Dipyridyl, however, enhances phenol formation from all three carbonacylanilides, but does not affect that from methanesulfonanilide.

2,2'-Dipyridyl

New chromogenic and fluorogenic substrates for pyrrolidonyl peptidase.

L-Pyroglutamyl derivatives of p-nitroaniline and 7-amino-4-methylcoumarin were synthesized as new sensitive substrates for pyrrolidonyl peptidase (pyrrolidonecarboxylyl peptidase) from Bacillus amyloliquefaciens. Their hydrolyses could be followed by conventional colorimetric and fluorometric procedures; i.e., in terms of the increase in absorbance at 410 nm caused by the liberation of p-nitroaniline and the emission at 440 nm after excitation at 370 nm depending on the liberation of 7-amino-4-methylcoumarin. Values of Km were estimated to be 0.69 mM for anilide substrate and 0.33 mM for methylcoumarin substrate in the pyrrolidonyl peptidase reaction at pH 8.0. The methylcoumarin compound was about one thousand fold more sensitive than the anilide substrate.

Aminopeptidases

Do cleavages of amides by serine proteases occur through a stepwise pathway involving tetrahedral intermediates?

The mechanism of the serine protease-catalyzed cleavage of amides (acylation) was examined in terms of the basicity of the functional groups participating in the catalysis. It is proposed that the reaction does not proceed through a stepwise pathway, as opposed to the cleavage of esters and anilides, which start with general base-catalyzed formation of the tetrahedral intermediate followed by its general acid-catalyzed breakdown. Instead, the proton abstracted from the hydroxyl group of the serine by the imidazolyl group of the histidine is donated to the nitrogen atom of the leaving group of the amide before the bond between the carbonyl carbon atom of the amide and the attacking serine oxygen atom is completed. Reactions proceed by a SN2-like reaction through the cooperation of acid catalysis by the imidazolyl cation and nucleophilic attack by the serine. The mechanisms of the enzymatic hydrolyses of anilides and esters proceed through a discrete tetrahedral intermediate, but the enzymatic hydrolyses of amides probably do not.

Amides

Kinetic studies of carboxypeptidase Y. I. Kinetic parameters for the hydrolysis of synthetic substrates.

Kinetic parameters for carboxypeptidase Y [EC 3.4.12.1], characterized as a nonspecific enzyme, are given for the hydrolysis of a series of acylated peptides, acylated amino acid esters, and amides. We confirmed that the enzyme released COOH-terminal proline and beta-alanine at an appreciable rate, as well as neutral amino acids with aromatic and aliphatic side chains at a very high speed. The rates of hydrolysis of ester and amide substrates were compatible with those produced by chymotrypsin [EC 3.4.21.1]. Stereospecificity was also demonstrated by the failure to hydrolyze peptide, ester, amide, and anilide substrates containing a D-amino acid. The effects of pH, solvents, and salt concentrations on the kinetic parameters of hydrolysis of peptide and ester substrates are also described.

Anilides

Components of the kallikrein-kinin system in urine.

The excretion of kallikrein in urine varies, but the pathophysiologic implications are not clear. To help clarify the role of the urinary kallikrein-kinin system, we have begun to define components of the system as they occur in urine. To minimize artifacts which may arise through extensive purification procedures, we studied urinary protein concentrates prepared by ultrafiltration. The concentrates were separated by chromatography on Sephacryl. Urine contains abundant kininase activity, but in strongly inhibited forms. Kininase II is separable into at least two forms. Another major kininase can hydrolyze benzoyl-Pro-Phe-Arg and is inhibited by arginine but not by BPP9a or SQ 14,225. Its molecular weight is approximately 63,000. A third kininase, not inhibited by BPP9a, is excluded from Sephacryl. Human urine appears to contain only one kallikrein-like enzyme (MW 45,000). In addition, urine contains a protein (MW approximately 80,000) which reacts with trypsin to release bradykinin and which inhibits the hydrolysis of Pro-Phe-Arg-[3H]anilide by urinary kallikrein. Thus, in addition to kallikrein and kinins, urine contains kininogen and at least three kininase enzymes. Urinary ultrafiltrate contains an inhibitory substance (approximately MW 400).

Animals

Isolation and characterization of an enkephalin-degrading aminopeptidase from rat brain.

An enkephalin-degrading aminopeptidase from rat brain extracts has been purified to apparent homogeneity. This enzyme cleaves the N-terminal tyrosine from Leu-enkephalin and hydrolyzes some beta-naphthylamides and p-nitro-anilides of neutral, basic and aromatic, but not acidic, amino acids. The enzyme requires a free amino group on the substrate and has a neutral pH optimum. After dialysis against EDTA, the enzyme requires a divalent cation (Zn2+, Co2+ greater than Mn2% greater than Mg2+) for activity. The enzyme is inhibited by puromycin, o-phenanthroline, p-chloromercuribenzoate and EDTA, but not by puromycin, methylsulfonyl fluoride or a specific peptide inhibitor of leucine amino-peptidase. The aminopeptidase consists of two subunits and has a molecular weight of about 100 000.

Aminopeptidases

Studies on the catalytic action of poly-alpha-amino acids. VII. Stereospecificity in the enzyme-like hydrolysis of benzoyl-L-(D)-arginine-p-nitroanilides by copoly (Cys, Glu).

The substrate specificity in the hydrolysis of L-, DL-, and D-BAPA (benzoylarginine-p-nitro-anilide) by copoly (L-Cys, L-Glu) and copoly (D-Cys, D-Glu) was studied, and enzyme-like stereospecific hydrolyses by poly-alpha-amino acids were identified for the first time. The L-type copolymer hydrolyzed L-BAPA faster than D-BAPA and the rates (v) of BAPA hydrolyses by L-type copolymer were found to be in the order vL greater than vDL greater than vD. On the other hand, the D-type copolymer hydrolysed D-BAPA faster than L-BAPA and the rates of BAPA hydrolyses by D-type copolymer were in the order vD greater than vDL greater than vL. In all cases, the reaction followed Michaelis-Menten kinetics when the substrate concentration was corrected, and the optimum conditions of the reaction were pH 6.0 and 40 degrees. The activity appeared after a certain amount of BAPA had combined with the polymer. D- and L-substrates combine competitively with the polymer and the different rates of hydrolysis are presumably due to the different substrate configurations in relation to the conformation of the active site in the polymer. The polymer shows activity near the range of random coil conformation, where some alpha-helical conformation is still present. Only some of the cysteine residues in the copolymer are involved in the hydrolytic activity.

Arginine

Endothelial cells and components of the kallikrein-kinin system.

Endothelial cells are a major source of kininase enzymes including kininase II. Kininase II is situated along the plasma membrane, not as an ecto-enzyme but as an enzyme synthesized by the endothelial cells themselves. However, it is likely that endothelial cells do more than degrade kinins. These cells are contractile and may possess kinin receptors; a possibility supported by the fact that kinins stimulate endothelial cells to form and release prostaglandin-related substances. In addition, we have found that endothelial cells in culture are reactive with antibodies to alpha 2-macroglobulin. Endothelial cells can hydrolyze [3H]Pro-Phe-Arg-anilide, a kallikrein substrate, but the reaction is not inhibited by soya bean trypsin inhibitor (SBTI) or Trasylol. Possibly kallikrein or a related trypsin-like enzyme is bound to alpha 2-macroglobulin and is not free to react with the inhibitors. Thus, endothelial cells can bind and inhibit kallikrein-like enzymes, degrade kinins and respond to kinin stimulation.

Animals

Gamma glutamyl transferase: application of a new radiochemical assay to the analysis of its subcellular distribution in the rat liver.

gamma-Glutamyl transferase (gamma-GT) is a key catalyst in the metabolism of glutathione. Its activity in the rat liver is usually very low but it increases significantly during the process of chemical hepatocarcinogenesis. A new radiochemical assay is reported which measures the amount of 3H-aniline liberated from gamma-glutamyl-3H-anilide. This assay is highly specific and no biological substances interferes. By applying this new assay to the analysis of the subcellular distribution of the rat liver gamma-GT, it is shown that it distributes between two pools, one which corresponds to a membrane-bound enzyme, the other to a soluble enzyme. The subcellular distribution of gamma-GT is discussed by comparison with the patterns of distribution of classical marker enzymes.

Animals

Synthetic analgesics: N-(1-[2-arylethyl]-4-substituted 4-piperidinyl) N-arylalkanamides.

The synthesis of several 4-arylamino-4-piperdinecarboxylic acids is reported. These acids were starting materials for the preparation of alpha-amino esthers, ethers and ketones. Different synthetic approaches are described. Suitable substitution on both nitrogen atoms afforded extremely potent analgesics. Thus, methyl 4-[N-(1-oxopropyl)-N-phenylamino]-1-(2-phenylethyl)-4-piperidinecarboxylate (22),N-(4-(methoxymethyl)-2-[2-(2-thienyl)ethyl]-4-piperidinyl)-N-phenylpropranamide (67) and N-[4-acetyl-1-(2-phenylethyl)-4-piperidinyl]-N-phenylpropanamide (82) were found to be respectively 7682, 3987 and 4921 times as potent as morfine. Both cis- and trans-3-methyl homologs of 22 have been prepared. As expected, analgesic activity resides mainly in the cis-isomer.

Analgesia

Application of trihydroxyindole reaction to methanesulfonanilides: fluorometric analysis for soterenol and mesuprine.

Methanesulfonanilides, like soterenol and mesuprine, which are bioisosteric with adrenergic catecholamines, form fluorescent species when subjected to the trihydroxyindole reaction. Presumably, the fluorescence is due to adrenolutin-like species formed from aminochrome intermediates. Fluorescence was not induced in a relative of soterenol where a methyl group was added to the sulfonamido nitrogen, a fact that suggests the presence of a quinoid intermediate in the reaction scheme of soterenol. A ring isomer of soterenol, where the methanesulfonamido and hydroxyl groups were interchanged, produced only about 5% as much fluorescence response as soterenol. The sterenol counterparts to isoproterenol and isoproterenol sulfonic acid did not produce fluorescence when treated like soterenol. This finding and the fact that response was linear with concentration for soterenol and mesuprine suggest that a fluorometric analysis could be developed for these methanesulfonanilides.

Anilides

Light and electron histochemistry of phosphoamidase with p-chloranilidophosphonic acid and with cyclophosphamide (endoxan).

The original metal-salt technique of Gomori (1948a) employing p-chloranilidophosphonic acid as a substrate for the demonstration of the activity of phosphoamidase has been used with varying success by a number of investigators for light microscopy. Cyclophosphamide (endoxan) which is a cytotoxic drug known to activate phosphoamidase and other lysosomal enzymes in neoplasm (Grillo, 1971) is proposed as another substrate for the enzyme for both light and electron microscopy.

Anilides

Clinical experience of encainide (MJ 9067): a new anti-arrhythmic drug.

Encainide is a new anti-arrhythmic drug, which is highly effective against ventricular extrasystoles, both single and coupled, in the dose range of 80--140 mg i.v. Ventricular extrasystoles were abolished in 31 out of 33 cases treated. The drug is also relatively effective against supraventricular extrasystoles, but has little effect on atrial fibrillation. Both subjects with clinically normal hearts and those with ischaemic heart disease have been successfully treated. The drug prolongs the QRS and QT duration. Its effectiveness appears to be of the same order of magnitude and the range of indications similar to those of aprindine and lorcainide. Further study of the drug seems to be warranted.

Anilides