Hormozgan Med J. 2019 March; 23(1):e88269. Published online 2019 February 13. doi: 10.5812/hmj.88269. Research Article Scopoletin and Morin Inhibit Lactate Dehydrogenase Enzyme Activity, Which Is Critical for Cancer Metabolism Melika Mazlaghaninia 1 , Maliheh Sadat Atri 1, * and Bagher Seyedalipour 1 1 Department of Molecular and Cell Biology, Faculty of Basic Sciences, University of Mazandaran, Babolsar, Iran * Corresponding author: Department of Molecular and Cell Biology, Faculty of Basic Sciences, University of Mazandaran, Babolsar, Iran. Tel: +98-1135302407, Fax: +98-1135302450, Email: m.atri@umz.ac.ir Received 2018 December 25; Accepted 2018 December 25. Abstract Background: Lactate dehydrogenase (LDH) is a tetrameric enzyme that catalyzes the interconversion of pyruvate to L-lactate. The importance of this enzyme is because LDH isoenzymes are involved in cancer, heart, and liver diseases. Inhibition of this enzyme can help prevent and treat different diseases. Morin is a flavonoid found in the Moraceae family and scopoletin is a coumarin found in Scopolia genus. Objectives: The aim of this study was to determine the effect of morin and scopoletin as two natural products on the activity and structure of lactate dehydrogenase enzyme. Methods: Morin and scopoletin were examined for inhibition of the activity of LDH in 100 mM sodium phosphate buffer pH 7.5, at room temperature using UV-V spectrophotometry. Fluorescence spectroscopy was used to characterize protein structural changes in the presence of morin and scopoletin. Results: Km and Vmax of LDH for pyruvate were 11.69 mM and 1.258 mM/min, respectively. The kinetic results showed that morin and scopoletin are LDH inhibitors. The Ki values of morin and scopoletin were determined as 1.78 μM and 0.8 μM, respectively, using a secondary plot. Fluorescence intensity quenching and red shift of the maximum wavelength of emission in a concentration- dependent manner showed that morin and scopoletin bind to LDH and affect its structure. Conclusions: The results suggest that morin and scopoletin bind to LDH, influence its conformation and inhibit its activity. Scopo- letin showed more effective inhibition of LDH activity and it can be a promising candidate in the field of tumor metabolism in- hibitors. Keywords: Lactate Dehydrogenase, Morin, Scopoletin, Spectrophotometry, Enzyme inhibitors 1. Background Lactate dehydrogenase (LDH, EC 1.1.1.27) is a key enzyme in anaerobic respiration that catalyzes the reversible con- version of pyruvate to lactate in the presence of NADH. Two major forms of LDH found in a wide range of organisms are the A form (A4-LDH), found predominantly in anaer- obic tissues, such as skeletal muscle and liver, and the H form (B4-LDH), which predominates mainly aerobic tis- sues, such as the heart (1, 2). A third type has also been identified, the X form, which appears to be restricted to the testes (3). The LDH-A and LDH-B subunits are similar in size and share 75% sequence identity yet have different catalytic properties; the A subunit preferentially converts pyruvate to lactate, while for the B form the opposite is true. They or- ganize four distinct enzyme classes with tetrameric struc- ture; A4, A3B, A2B2, B3A, and B4 that are different isoen- zymes of LDH (4). Furthermore, LDH is a biomarker of dif- ferent diseases, thus this enzyme is an interesting enzyme for scientists. Since metabolism is impaired in cancer cells, these cells are dependent on anaerobic metabolism to survive. Lactate dehydrogenase inhibition could be the target of different cancer therapy studies. Inhibition of LDH devas- tate glucose metabolism in cancer cells without affecting the energetic balance of normal cells. Inactivation of LDH enzyme in the presence of different natural and synthetic components has been studied. For example, Galloflavin is a synthetic compound that inhibits both A and B iso- forms of LDH and hinders the proliferation of tumor cells by blocking glycolysis. The inhibition is a mixed type for pyruvate and lactate (5). FX11 [3-dihydroxy-6-methyl-7- (phenylmethyl)-4-propylnaphthalene-1-carboxylic acid] is another inhibitor of LDH that used for treatment of pan- creatic cancer in vivo and in vitro (2). Genistein is an- other LDH inhibitor that inhibits the activity of enzyme due to competition with NADH for the enzyme binding (6). Modification of LDH enzyme can induce conformational Copyright © 2019, Hormozgan Medical Journal. This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International License (http://creativecommons.org/licenses/by-nc/4.0/) which permits copy and redistribute the material just in noncommercial usages, provided the original work is properly cited.