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
(O2-.) (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 350C to 400C
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+>Ba2+>Ca2+>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.