Kinetics of DPPH. scavenging by bacterioruberin from Haloferax alexandrinus GUSF-1 (KF796625)

Abstract

This is the first account of the kinetics of free radical scavenging by bacterioruberin obtained from cells of Haloferax alexandrinus GUSF-1(KF796625), grown at optimum conditions of 25 percent NaCl, pH 7, 42 degrees C, 150 rpm in NaCl Tryptone yeast extract medium and light. Bacterioruberin separated from methanolic extract displayed characteristics absorption peaks at 368, 386, 463, 492 and 525 nm and gave an m/z value of 740.4 (C sub(50) H sub(76) O sub(4)) in Liquid Chromatography-Mass Spectroscopy validating its purity. Bacterioruberin (13 Mu M) decolorized and decayed 0.2 mM 1,1-diphenyl-2-picrylhydrazyl radicals (DPPH.) monitored at 517 nm and reached a steady state within 30 min. An EC sub(50) of 6.50 Mu M plus or minus 0.27 (4.81 mu g/mL plus or minus 0.2) was deduced for the 0.2 mM DPPH.-bacterioruberin reaction using the GraphPad Prism 9 statistical software and employing the right-angled triangle technique. The study also revealed a comprehensive information of the total kinetic activity of bacterioruberin with DPPH.: the antioxidant activity index was 16.38 plus or minus 0.67; time needed to reach the steady state with the added EC sub(50)-30 min; the antiradical power 30.77 plus or minus 1.27 and the antiradical efficiency of 54.7 x 10-3 plus or minus 2.24, thus reflecting the strong antioxidant nature of bacterioruberin. Scavenging of DPPH. by bacterioruberin was a pseudo-first-order reaction with a rate constant k sub(2) of 2.76 x 10-5 plus or minus 0.001 mu M-1 s-1 calculated at t=0 or initial time and t=30 min. The knowledge of the kinetics of bacterioruberin to scavenge DPPH. adds to its effective application as an antioxidant in medicinal use, pharmaceutical products and others. Additionally, the use of simple conventional method of DPPH. free radical scavenging, monitored using an easily available laboratory spectrophotometer, will certainly help in the effective use of any antioxidant compound.