Introduction & Objectives: The LDH (Lactate Dehydrogenase) catalyzes the reversible transformation of pyruvate to lactate under anaerobic conditions, coupled with the oxidation of NADH to NAD+. Each normal tissue has a distinct LDH activity pattern, depending on their functions and levels of LDH increase in response to tissue injury, necrosis, hypoxia,. LDH is a homo- or heterotetramer assembled from two types of subunit: LDHA(M) and LDHB(H) that organize the five major isozyme of LDH: LDH1 to LDH5. LDH related to different diseases including cancers. LDH upregulation facilitates the efficiency of anaerobic glycolysis in tumor cells. FX11 is an inhibitor of LDH for the treatment of pancreatic cancer has been studied. Other inhibitors of this enzyme can be oxamate, Gossypol, Galloflavin. With using inhibitors we can inhibit diseases. Morin is a natural compound isolated from herbs used in traditional Chinese medicine. Morin is a potent inhibitor of Xanthine Oxidase, Urate Oxidase. According to the studies we investigate the effect of morin on LDH structure. Methods: In this study, Intrinsic fluorescence was determined using an excitation wavelength of 280 nm and the emission spectra were recorded between 300 and 500 nm at temperatures of 25 °C on a Cary-Eclipse spectrofluorometer, in presence of different concentrations of morin. Results: The fluorescence intensity of LDH decreased regularly upon each addition of morin. Since quenching of LDH with an increasing LDH /morin ratio, then the morin interaction with LDH changed the microenvironment of Trp residue(s). Conclusion: Due to reduced absorption reactions in the presence of morin can be concluded that this substance changed the conformation of LDH.
