Effect of Spirulina platensis crude extract on catalase activity and stability

Spirulina platensis has recently received considerable attention because of its potential application in the prevention and/or management of cancer and many other diseases. However, little is known about the effects of S. platensis on the antioxidant defense system. 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. Spectrophotometric methods were executed to understand S. platensis -induced alterations in catalase. Results showed that low concentrations of S. platensis extracts stimulated catalase activity, whereas higher concentrations inhibited its 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 indicated that the binding reaction is a spontaneous and exothermic process, and hydrogen bonds and van der Waals forces play a major role in binding the compounds in S. platensis extract to catalase. The number of obtained binding sites was ~2. Circular dichroism spectroscopy data showed that high concentrations of S. platensis extract led to a significant decrease in α-helix and ß-sheet content, accompanied by an increase in the enzyme’s random coil content. 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.