Use of mushroom tyrosinase to introduce michaelis-menten enzyme kinetics to biochemistry students

A novel method for explaining the product inhibition mechanisms via molecular docking: inhibition studies for tyrosinase from Agaricus bisporus

The present study aims to investigate the substrate (4-methyl catechol and catechol) specificity and inhibition mechanisms (l-ascorbic acid, citric acid, and l-cysteine) of the tyrosinase enzyme (TYR), which is held responsible for browning in foods and hyperpigmentation in the human skin, through kinetic and molecular docking studies. During the experimental studies, the diphenolase activities of TYR were determined, following which the inhibitory effects of the inhibitors upon the diphenolase activities of TYR. The inhibition types were determined as competitively for l-ascorbic acid and citric acid and noncompetitive for l-cysteine. The kinetic results showed that the substrate specificity was better for catechol while l-cysteine showed the best inhibition profile. As for the in silico studies, they also showed that catechol had a better affinity in line with the experimental results of this study, considering the interactions of the substrates with TYR's active site residues and their distance to CuB metal ion, which is an indicator of diphenolase activity. Besides, the inhibitory mechanisms of the inhibitor molecules were explained by the molecular modeling studies, considering the binding number of the inhibitors with the active site amino acid residues of TYR, the number and length of H bonds, negative binding energy values, and their distance to CuB metal ion. Based on our results, we suggest that the novel method used in this study to explain the inhibitory mechanism of l-cysteine may provide an affordable alternative to the expensive methods available for explaining the inhibitory mechanism of TYR and those of other enzymes. HighlightsThe best affinity for the tyrosinase enzyme occurred with catechol.l-Ascorbic acid, citric acid, l-cysteine inhibited the diphenolic activity of tyrosinase.In silico studies confirmed the best affinity shown by catechol.Product inhibition mechanism of l-cysteine explained by in silico for the first time.Communicated by Ramaswamy H. Sarma.

Laboratory Exercise To Measure Restriction Enzyme Kinetics

Enzymes are ubiquitous in the fields of biology and microbiology, catalyzing critical reactions and enabling a broad range of biotechnological applications. Despite the important role that enzyme catalysis plays in biological processes, undergraduate students often struggle to understand enzyme kinetics in the classroom. In an attempt to improve students’ understanding of the topic, we present a relatively short and inexpensive laboratory activity designed to give students hands-on experience with generating and manipulating enzyme kinetic data. Students perform restriction digests of DNA at various time points, visualize the reaction products on an agarose gel, and quantify their data in order to construct Lineweaver-Burk plots which compare the effects of a restriction enzyme and its engineered version. The activity may be completed in a single two-hour lab session and, unlike other enzyme assays designed for laboratory courses, does not require a microplate reader to complete. The activity allows students to see connections between a visual data set and quantitative kinetic data, in order to solidify their understanding of enzyme kinetics. Students also learn the skills of gel electrophoresis and image quantification using ImageJ software. This lab activity is ideal for undergraduate laboratory courses which address enzyme kinetics and DNA technology.