RESUMO
The weakness of firefly luciferase is its rapid inactivation. Many studies have been done to develop thermostable luciferases. One of these modifications was LRR mutant in which the Leu300 was substituted with Arg in the E(354)RR(356)Lampyris turkestanicus luciferase as template. LRR was more thermostable than the wild type but with only 0.02% activity. In this study, site-directed mutagenesis was used to change the proposed ionic bond between the Arg and two neighboring residues (Glu270 and Glu271), to understand if the induced interactions were responsible for inactivation in LRR. Our results showed that substitution of Glu270 and 271 with Ala removed the interactions but the activity of enzyme did not return. The E270A mutant was more active than LRR but the E271A and E270A/E271A mutants were inactive. Fluorescence and CD measurements showed that these mutations were accompanied by conformational changes. Extrinsic fluorescence measurement and obtained quenching data by KI and acrylamide also confirmed that the mutants were less compact than the LRR enzyme. In conclusion, in LRR, the interactions between Arg300 and Glu270 and Glu271 were not responsible for the enzyme inactivation and it is proposed that the enzyme inactivation is due to conformational changes of LRR mutant of firefly luciferase.
Assuntos
Luciferases de Vaga-Lume/antagonistas & inibidores , Luciferases de Vaga-Lume/genética , Substituição de Aminoácidos , Animais , Estabilidade Enzimática , Vaga-Lumes/enzimologia , Vaga-Lumes/genética , Interações Hidrofóbicas e Hidrofílicas , Proteínas de Insetos/antagonistas & inibidores , Proteínas de Insetos/química , Proteínas de Insetos/genética , Cinética , Luciferases de Vaga-Lume/química , Modelos Moleculares , Mutagênese Sítio-Dirigida , Conformação Proteica , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Espectrometria de FluorescênciaRESUMO
BACKGROUND: Methocarbamol is a skeletal muscle relaxant and is widely used to relieve pain in muscles. Many drugs may have interactions with each other when used at the same time. Yeast sucrase is taken as a drug by patients with congenital sucrase-isomaltase deficiency (CSID). METHODS: In this study, the interaction between methocarbamol and yeast sucrase was investigated. RESULTS: Our results showed that methocarbamol can inhibit sucrase activity and reduce the maximum reaction velocity (Vmax) of the enzyme by a non-competitive pattern. Measurement of IC50 and Ki of the drug revealed that methocarbamol did not bind the enzyme with high affinity. Fluorescence measurement showed that the drug binds to free enzyme and enzyme-substrate complexes that were accompanied by structural changes on the enzyme. Guaifenesin, which has a similar structure to methocarbamol, does not affect the activity of sucrase. CONCLUSIONS: Methocarbamol inhibits sucrase activity and its carbamate group plays a main role in the binding of drug to sucrase.
Assuntos
Inibidores Enzimáticos/farmacologia , Metocarbamol/farmacologia , Sacarase/antagonistas & inibidores , Leveduras/enzimologia , FluorescênciaRESUMO
Ranitidine is an antagonist of histamine-2 (H(2)) receptor. It is employed to treat peptic ulcer and other conditions in which gastric acidity must be reduced. Sucrase is a hydrolytic enzyme that catalyzes the breakdown of sucrose to its monomer content. A liquid of yeast sucrase was developed for treatment of congenital sucrase-isomaltase deficiency (CSID) in human. In this study, the effect of ranitidine on yeast sucrase activity was investigated. Our results showed that ranitidine binds to sucrase and inhibits the enzyme in a noncompetitive manner. The K(i) and IC(50) values were measured to be about 2.3 and 2.2 mM, respectively. Fluorescence measurement showed conformational changes after binding of ranitidine to the enzyme. The fluorescence spectra showed that ranitidine could bind to both free enzyme and enzyme-substrate complex, which was accompanied with reduction of emission intensity and red shift production.
Assuntos
Inibidores Enzimáticos/farmacologia , Ranitidina/farmacologia , Sacarase/antagonistas & inibidores , Sacarase/química , Relação Dose-Resposta a Droga , Inibidores Enzimáticos/química , Conformação Proteica/efeitos dos fármacos , Ranitidina/química , Saccharomyces cerevisiae/enzimologia , Relação Estrutura-Atividade , Sacarase/metabolismoRESUMO
Scopolamine (hyoscine) is commonly used as an anticholinergic drug to relieve nausea, vomiting and dizziness of a motion sickness as well as recovery from anesthesia and surgery. Sucrase as a hydrolytic enzyme breaks down sucrose into its monomers, glucose and fructose. The aim of this study was to evaluate the effect of scopolamine on the activity and the structural changes of yeast sucrase. The results showed that binding of scopolamine to sucrase could inhibit the enzyme activity. A non-competitive inhibition was observed in different concentrations of scopolamine (0.6 to 3.6mM). The study by circular dichroism measurement in far-UV showed that the absolute enzyme exhibited a flat negative trough, indicating the presence of alpha-helices and beta-sheet structures in the enzyme. Binding of the inhibitor on the enzyme made a deeper trough at 218nm, suggesting the increasing of beta-sheet content of the enzyme. Fluorescence measurement showed that binding of scopolamine to free enzyme and enzyme-substrate complex increased the peak intensity at 350nm and also induced red shift. Our findings suggest that scopolamine binds to the location other than the active site of enzyme and that the binding causes structural changes and inhibits the enzyme activity.