Kinetic and Biochemical Parameters of Thermostable Superoxide Dismutase Isolated from Ribes nigrum: A Functional Food

Abstract

Oxidative stress, induced by oxygen free radicals (Reactive oxygen species: ROS), is believed to be a primary factor in various degenerative diseases. Co-operative defense systems that protect the body from free radical damage include the anti-oxidant nutrients and enzymes. Superoxide free radical (O 2-. ) (ROS) is a strong oxidant and damage other molecules and the cell structures of which they are a part. Superoxide Dismutase (SOD: 1.15.1.1) is an ubiquitous, powerful antioxidant enzyme which catalyzes the dismutation of the super oxide radical into hydrogen peroxide and molecular oxygen and plays a central role in protecting against oxidative stress. In the present study, thermostable SOD has been isolated and characterized from Ribes nigrum; a dry fruit. The SOD enzyme obtained has been partially purified into two fractions based on 0-40% and 40- 80% saturation level of ammonium sulphate; 0-40% fraction (66.5 Units/mg) having higher specific activity. The temperature optima of the partially purified SOD lied between 35 0 C to 40 0 C with thermostability up to 70°C whereas the optimum value for pH being 6.0 with stability range of 5.0-7.0. Amongst the tested detergents; the enzyme inhibition was found in the descending order as Sodium Lauryl Sulphate (SLS), Tween-20 and Tween- 80. Cween-20 did not affect the activity of enzyme. Various univalent and bivalent ions in the form of their respective salts were used to perform inhibition studies. They were found to inhibit SOD activity in the given order: Na + >Ba 2+ >Ca 2+ >K + . Barium and Sodium ions showed about 50% reduction in enzyme activity with inhibition constants (Ki) values being 2.4 mM and 1.6 mM, respectively. The results obtained herein indicate that R. nigrum being an excellent source of natural dietery antioxidant enzyme, has great potential as functional food. It can be inferred from the present study that R. nigrum, a dry fruit rich in sugars and other nutrients, is also a promising source of SOD, which in turn has application in oxidative stress-related diseases. The thermo-stability of the enzyme further enhances its importance making it industry friendly with high economical feasibility. Further studies are needed to explore the potential of such therapeutically important products, along with their use as supplement in various medicinal formulations.