ABSTRACT
Peptidyl alpha-hydroxylating monooxygenase (PHM) functions in vivo towards the biosynthesis of alpha-amidated peptide hormones in mammals and insects. PHM is a potential target for the development of inhibitors as drugs for the treatment of human disease and as insecticides for the management of insect pests. We show here that relatively simple ground state analogs of the PHM substrate hippuric acid (C(6)H(5)-CO-NH-CH(2)-COOH) inhibit the enzyme with K(i) values as low as 0.5microM. Substitution of sulfur atom(s) into the hippuric acid analog increases the affinity of PHM for the inhibitor. Replacement of the acetylglycine moiety, -CO-NH-CH(2)-COOH with an S-(thioacetyl)thioglycolic acid moiety, -CS-S-CH(2)-COOH, yields compounds with the highest PHM affinity. Both S-(2-phenylthioacetyl)thioglycolate and S-(4-ethylthiobenzoyl)thioglycolic acid inhibit the proliferation of cultured human prostate cancer cells at concentrations >100-fold excess of their respective K(i) values. Comparison of K(i) values between mammalian PHM and insect PHM shows differences in potency suggesting that a PHM-based insecticide with limited human toxicity can be developed.
Subject(s)
Enzyme Inhibitors/chemistry , Hippurates/chemistry , Hippurates/pharmacology , Insecticides/chemistry , Mixed Function Oxygenases/antagonists & inhibitors , Multienzyme Complexes/antagonists & inhibitors , Animals , Antineoplastic Agents/chemical synthesis , Antineoplastic Agents/chemistry , Antineoplastic Agents/pharmacology , Enzyme Inhibitors/chemical synthesis , Enzyme Inhibitors/pharmacology , Hippurates/chemical synthesis , Humans , Inhibitory Concentration 50 , Insecticides/metabolism , Insecticides/pharmacology , Mixed Function Oxygenases/metabolism , Models, Molecular , Multienzyme Complexes/metabolism , Rats , Structure-Activity Relationship , Tumor Cells, CulturedABSTRACT
Peptidyglycine alpha-amidating monooxygenase is a copper- and zinc-dependent, bifunctional enzyme that catalyzes the cleavage of glycine-extended peptides or N-acylglycines to the corresponding amides and glyoxylate. This reaction is a key step in the biosynthesis of bioactive alpha-amidated peptides and, perhaps, the primary fatty acids amides also. Two clinically useful N-acylglycines are thiorphan and tiopronin, each with a thiol moiety attached to the acyl group. We report here that thiorphan and tiopronin are substrates for PAM, exhibiting relatively low K(M,app) and V(MAX,app) values. The low V(MAX,app) values result, most likely, from a decrease in active PAM.2Cu(II) as the enzyme competes ineffectively with thiorphan and tiopronin for free copper.
Subject(s)
Mixed Function Oxygenases/antagonists & inhibitors , Mixed Function Oxygenases/metabolism , Multienzyme Complexes/antagonists & inhibitors , Multienzyme Complexes/metabolism , Protease Inhibitors/metabolism , Thiorphan/metabolism , Tiopronin/metabolism , Animals , Binding Sites , Copper/metabolism , Mixed Function Oxygenases/chemistry , Molecular Structure , Multienzyme Complexes/chemistry , Oxidation-Reduction , Protease Inhibitors/chemistry , Protein Structure, Tertiary , Rats , Thiorphan/chemistry , Tiopronin/chemistryABSTRACT
Ubiquitin (Ub) and the ubiquitin-like proteins (UBLs) mediate an array of cellular functions. These proteins contain a C-terminal glycine residue that is key to their function. Oxidative conversion of C-terminal glycine-extended prohormones to the corresponding alpha-amidated peptide is one step in the biosynthesis of bioactive peptide hormones. The enzyme catalyzing this reaction is peptidylglycine alpha-amidating monooxygenase (PAM). We report herein that Ub is a PAM substrate with a (V/K)(amidation) that is similar to other known peptide substrates. This work is significant because PAM and the UBLs co-localize to the hypothalamus and the adrenal medulla and are both over-expressed in glioblastomas.
Subject(s)
Mixed Function Oxygenases/metabolism , Multienzyme Complexes/metabolism , Peptides/metabolism , Ubiquitin/metabolism , Amino Acid Sequence , Animals , Cattle , Glycine/metabolism , Glyoxylates/metabolism , Molecular Structure , Oxidation-Reduction , Oxygen/metabolism , Peptides/genetics , Rats , Ubiquitin/geneticsABSTRACT
Oleamide is an endogenous sleep-inducing lipid that has been isolated from the cerebrospinal fluid of sleep-deprived mammals. Oleamide is the best-understood member of the primary fatty acid amide family. One key unanswered question regarding oleamide and all other primary acid amides is the pathway by which these molecules are produced. One proposed pathway involves oleoyl-CoA and N-oleoylglycine as intermediates: oleic acid --> oleoyl-CoA --> N-oleoylglycine --> oleamide. The first and third reactions are known reactions, catalyzed by acyl-CoA synthetase and peptidylglycine alpha-amidating monooxygenase (PAM). Oleoyl-CoA formation from oleic acid has been demonstrated in vitro and in vivo while, to date, N-oleoylglycine cleavage to oleamide has been established only in vitro. PAM catalyzes the final step in alpha-amidated peptide biosynthesis, and its proposed role in primary fatty acid amide biosynthesis has been controversial. Mouse neuroblastoma N(18)TG(2) cells are an excellent model system for the study of oleamide biosynthesis because these cells convert [(14)C]-oleic acid to [(14)C]-oleamide and express PAM in a regulated fashion. We report herein that growth of the N(18)TG(2) cells in the presence of [(14)C]-oleic acid under conditions known to stimulate PAM expression generates an increase in [(14)C]-oleamide or in the presence of a PAM inhibitor generates [(14)C]-N-oleoylglycine. This represents the first identification of N-oleoylglycine from a biological source. In addition, N(18)TG(2) cell growth in the presence of N-oleoylglycine yields oleamide. These results strongly indicate that N-oleoylglycine is an intermediate in oleamide biosynthesis and provide further evidence that PAM does have a role in primary fatty acid amide production in vivo.
Subject(s)
Neuroblastoma/metabolism , Oleic Acid/metabolism , Animals , Cell Differentiation , Cell Line, Tumor , Culture Media/chemistry , Enzyme Inhibitors/chemistry , Fatty Acids, Monounsaturated/chemistry , Glycine/analogs & derivatives , Glycine/metabolism , Mice , Mixed Function Oxygenases/antagonists & inhibitors , Mixed Function Oxygenases/biosynthesis , Multienzyme Complexes/antagonists & inhibitors , Multienzyme Complexes/biosynthesis , Neuroblastoma/enzymology , Neuroblastoma/pathology , Oleic Acids/biosynthesis , Oleic Acids/metabolism , Spectrometry, Mass, Electrospray Ionization , Substrate SpecificityABSTRACT
The C-terminal alpha-amide moiety of most peptide hormones arises by the posttranslational cleavage of a glycine-extended precursor in a reaction catalyzed by bifunctional peptidylglycine alpha-amidating monooxygenase (PAM). Glutathione and the S-alkylated glutathiones have a C-terminal glycine and are, thus, potential substrates for PAM. The addition of PAM to glutathione, a series of S-alkylated glutathiones, and leukotriene C(4) results in the consumption of O(2) and the production of the corresponding amidated peptide and glyoxylate. This reaction proceeds in two steps with the intermediate formation of a C-terminal alpha-hydroxyglycine-extended peptide. Amidated glutathione (gammaGlu-Cys-amide) is a relatively poor substrate for glutathione S-transferase with a V/K value that is 1.3% of that for glutathione. Peptide substrates containing a penultimate hydrophobic or sulfur-containing amino acid exhibit the highest (V/K)(app) values for PAM-catalyzed amidation. The S-alkylated glutathiones incorporate both features in the penultimate position with S-decylglutathione having the highest (V/K)(app) of the substrates described in this report.
