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Modification of arginines in bovine growth hormone.

Treatment of bovine growth hormone with 1,2-cyclohexanedione - in borate buffer - selectively modified 11.8 out of the 13 arginines in the molecule. Kinetic analysis of the data showed a good fit to a pseudo first-order curve, with an apparent velocity constant k: 2 X 10(-2) min-1. The modification brought about a complete loss of bovine growth hormone capacity to compete with 125I-labelled hormone for rat liver binding sites. Circular dichroism studies indicated no apparent changes in protein conformation in the modified hormone. Full binding capacity was restored upon regeneration of arginines by hydroxylamine treatment. These results suggest that one or more arginines are involved in the binding of bovine growth hormone to its specific receptors. The non-reactive arginine was identified as arginine 181.

Amino Acids↗

Modification of arginine-198 in sarcoplasmic reticulum Ca2+-ATPase by 1,2-cyclohexanedione causes inhibition of formation of the phosphoenzyme intermediate from inorganic phosphate.

Sarcoplasmic reticulum vesicles were modified with 1,2-cyclohexanedione (CHD), a specific arginine-modifying reagent, in sodium borate (pH 8.0 or 8.8). Phosphoenzyme formation from Pi in the Ca2+-ATPase (reversal of hydrolysis of the phosphoenzyme intermediate) was almost completely inhibited by the modification with CHD. Tight binding of F- and Mg2+ and high affinity binding of vanadate in the presence of Mg2+, either of which produces a transition state analog for phosphoenzyme formation from the magnesium-enzyme-phosphate complex, were also markedly inhibited. In contrast, phosphoenzyme formation from acetyl phosphate in the forward reaction was unaffected. The enzyme was appreciably protected by tight binding of F- and Mg2+ or by high affinity binding of vanadate in the presence of Mg2+, but not by the presence of 20 mM MgCl2 alone or 150 mM Pi alone, against the CHD-induced inhibition of phosphoenzyme formation from Pi. Peptide mapping of the tryptic digests, detection of peptides containing CHD-modified arginyl residues with Girard's reagent T, sequencing, and mass spectrometry showed that Arg-198 was a single major residue protected by tight binding of F- and Mg2+ against the modification with CHD. These results indicate that modification of Arg-198 with CHD is responsible for at least a part (the portion reduced by the transition state analogs) of the CHD-induced inhibition of phosphoenzyme formation from Pi and suggest that Arg-198 is located in or close to the catalytic site in the transition state for phosphoenzyme formation from the magnesium-enzyme-phosphate complex.

Amino Acid Sequence↗

Modification of arginine residues in porcine pancreatic phospholipase A2.

Although phenylglyoxal monohydrate reacts with Arg-6 in porcine pancreatic phospholipase A2, concomittantly the alpha-amino group of the N-terminal Ala-1 residue is quantitatively transaminated. Due to this latter reaction the enzymatic activity toward micellar substrate is lost irrespective of the Arg-6 modification. Upon reaction of [7-(14)C]phenylglyoxal monohydrate with alpha-amino-blocked phospholipase A2 analogs, two molecules of the reagent were incorporated per protein molecule, which were found to be present on Arg-6. Removal of alpha-amino-blocking groups after the modification reaction furnished the corresponding Arg-6-modified phospholipases possessing 30-38% of their original specific enzymatic activities in the egg-yolk assay. After reaction of 1,2-[1-(14)C]cyclohexanedione with porcine phospholipase A2 the crude reaction mixture was purified by chromatography on quaternary diethyl-(2-hydroxypropyl)aminoethyl-Sephadex in the presence of borate. A fraction was obtained containing a pure protein in which one molecule of 14C-labeled reagent per protein molecule was incorporated which was found to be localized almost exclusively on Arg-6. Cyclohexanedione modification of Arg-6 in phospholipase A2 does not significantly influence its catalytic activity when assayed toward monomeric and micellar substrates. The results of direct binding experiments using substrate analogs and of monolayer studies of the phospholipase modified at Arg-6 by cyclohexanedione are in agreement with previous findings that Arg-6 is involved in the interaction of the enzyme with lipid-water interfaces.

Aldehydes↗

NMR evidence for perturbation of the copper coordination sphere upon chemical modification of arginine 141 in bovine Cu,Zn superoxide dismutase.

The reaction of the Cu,Co derivative of bovine Cu,Zn superoxide dismutase with phenylglyoxal or butanedione, which are known to inactivate the enzyme by selectively binding to Arg 141, has been studied by 1H NMR. Several 1H NMR lines of the copper-liganding histidine residues were perturbed, reproducing an effect so far observed only in the case of binding of anions to this protein. The room temperature EPR spectrum of the modified Cu,Zn protein was altered very slightly, indicating that the geometry of the copper site was not grossly affected by the modification. NMR and EPR changes were reversed by dialysis in the case of the reversible butanedione adduct. These data show that the coordination of the copper in Cu,Zn superoxide dismutase can be destabilized by modifications occurring at a neighboring but not a metal-liganding residue. It is suggested that part of the NMR effects seen on copper ligands in the case of anion binding are produced by interaction of anions with Arg 141, rather than by direct ligand replacement.

Amino Acid Sequence↗

Covalent and noncovalent chemical modifications of arginine residues decrease dopamine transporter activity.

Rotating disk electrode voltammetry was used to measure dopamine (DA) transport in rat striatum and in human embryonic kidney cells expressing the rat dopamine transporter (DAT). The goals of this study were to determine 1) if arginine (Arg) selective agents could alter DA transport, and 2) if DA analogs and DAT inhibitors could attenuate the effects of these agents on the DAT. Phenylglyoxal (PG), Hill coefficient 2.5, and other Arg selective agents decreased DA transport velocities. DA, Hill coefficient 1.0, and its analogs 3-hydroxyphenethylamine and 4-hydroxyphenethylamine attenuated the effects of PG on the DAT while phenethylamine did not. The tropane-based DAT inhibitors cocaine, WIN 35065-2, and WIN 35428 also attenuated the effects of PG. Benztropine, GBR 12935, and GBR 12909 did not. Thus, Arg residues are important for DAT activity and the results suggest that DA and cocaine both interact with Arg residues. Structure-activity studies suggest that DA interacts with Arg through its catechol hydroxyl groups and cocaine through the ester linkage attached to carbon 2 of the tropane ring. The results that 1). DA and cocaine may interact with the same functionally important Arg residue at the DAT, and 2). some members of the tropane and 1,4-dialkylpiperazine classes of DAT inhibitors may interact differently with DAT-derived Arg residue(s) furthers the notion that DAT activity sparing antagonists of cocaine can be designed.

Animals↗

Cyclohexanedione modification of arginine at the active site of Aspergillus ficuum phytase.

Reaction of Aspergillus ficuum phytase with the arginine specific modifier 1,2-cyclohexanedione causes a rapid loss of activity. The inactivation can be partially reversed by 0.2 M hydroxylamine and exhibits pseudo-first order kinetics. The reaction order and second order rate constant of inactivation were 0.87 and 6.72 M-1 Min-1, respectively. Amino acid analysis of modified phytase indicates that about 7 arginine of the total 19 were modified. While the chymotryptic maps of treated and untreated phytase wer virtually identical, the tryptic maps had 4 peaks of altered mobility. An Arg containing tripeptide was identified in the phytase which is also present in other phosphohydrolases and may represent one of the labile Arg involved in the formation of the active site.

6-Phytase↗

Modification of arginines in D-beta-hydroxybutyrate dehydrogenase.

D-beta-Hydroxybutyrate dehydrogenase (D-3-hydroxybutyrate: NAD+ oxidoreductase, EC 1.1.1.30) is a lipid-dependent enzyme which has an absolute and specific requirement for phosphatidylcholine for function. Chemical derivatization studies using 1,2-cyclohexanedione, an arginine-specific reagent, have been carried out on the purified enzyme devoid of lipid as well as on the enzyme reactivated with phospholipid. Cyclohexanedione inactivated the active enzyme-phospholipid complex and the lipid-free enzyme was rendered inactivatable by phospholipid. From kinetic studies and by direct chemical derivatization studies with [1-14C]cyclohexanedione, we find that incorporation of a single cyclohexanedione molecule per enzyme monomer resulted in complete loss of enzymic activity. The presence of NADH or NAD+, cofactors for the enzyme, offered no protection for the rate of inactivation. The substrates beta-hydroxybutyrate and acetoacetate with or without coenzyme gave little or no protection. However, 2-methyl malonate, a competitive inhibitor for beta-hydroxybutyrate, strongly protected against inactivation. These studies indicate that: (1) a single arginine serves a vital role and is essential for function; (2) the arginine is located in the proximity of the substrate binding site.

Animals↗

Chemical modification of arginine and lysine residues in coenzyme-binding domain of carbonyl reductase from rabbit kidney: indomethacin affords a significant protection against inactivation of the enzyme by phenylglyoxal.

Carbonyl reductase from rabbit kidney was inactivated by phenylglyoxal (PGO) and 2,4,6-trinitrobenzenesulfonate sodium (TNBS). NADP+ protected the enzyme from the inactivations by PGO and TNBS, suggesting that essential arginine and lysine residues are located in coenzyme-binding domain of the enzyme. Judging from the effects of PGO-treated enzymes in the presence and in the absence of NADP+ on the fluorescence intensity of NADPH, one essential arginine residue in coenzyme-binding domain was found to have a role in the binding of NADPH to the enzyme. Indomethacin afforded a significant protection against inactivation of the enzyme by PGO, whereas it could not protect the enzyme from the inactivation by TNBS. It is reasonable to postulate that indomethacin interacts at least in part with or near one essential arginine residue in coenzyme-binding domain of carbonyl reductase from rabbit kidney.

Alcohol Oxidoreductases↗