Effect of Spirulina platensis crude extract on catalase activity and stability

S. platensis has received much recent attention because of its potential application in the prevention and/or managing of cancer, and many other diseases. However, little is known about the effects of S. platensis on the antioxidant defense system, therefore this study aimed to investigate the effects of this microalga on the function and structure of the antioxidant enzyme catalase. The catalase activity was measured under steady-state kinetic conditions. The spectrophotometric methods including ultraviolet-visible absorption, circular dichroism spectroscopy, and fluorescence spectroscopy executed to understand the S. platensis-induced alterations in catalase. The results showed that S. platensis extracts at low concentrations stimulated catalase activity, whereas at higher concentrations inhibited catalase activity in a non-competitive manner. Catalase activity was inhibited by 27% and 80% using the aqueous and methanol extract, respectively. The Stern-Volmer plots indicated that S. platensis methanolic extract quenched catalase fluorescence emission with both static and dynamic mechanisms. The values of thermodynamic parameters for the S. platensis extract-catalase complex indicated that the binding reaction is a spontaneous and exothermic process and hydrogen bonds and van der Waals forces play a major role in the binding of compounds in S. platensis extract to catalase. The number of binding sites was obtained ~2. Circular dichroism spectroscopy data represented that high concentrations of S. platensis extract lead to a significant decrease in the content of α-helix and ß-sheet (p < 0.05) accompanied an increase in random coil content of the enzyme. According to the results, it can be concluded that the application of S. platensis extract has a dual effect on the structure and function of catalase, stimulatory or inhibitory, depending on its concentration. Therefore, it may have potential benefits as an antioxidant or tumor suppressor.