Purification and characterization of a psychrophilic glutathione reductase from Antarctic ice microalgae Chlamydomonas sp. Strain ICE-L

Abstract

A psychrophilic glutathione reductase from Antarctic ice microalgae Chlamydomonas sp. Strain ICE-L was purified by ammonium sulfate fractionation and three steps of chromatography. The yield was up to 25.1%
of total glutathione reductase in the crude enzyme extract. The glutathione reductase activity was characterized by the spectrophotometric
method under different conditions. Purified glutathione reductase was separated by SDS-PAGE, which furnished a homogeneous
band. The native molecular mass of the enzyme was 115kDa. Apparent Km values for NADPH and NADH (both at 0.5mmolL−1 oxidized glutathione) were 22.3 and 83.8μmolL−1, respectively. It was optimally active at pH7.5, and it was stable from pH5 to 9. Its optimum temperature was 25°C, with
activity at 0°C 23.5% of the maximum. Its optimum ion strength and optimum Mg2+ were 50–90 and 7.5mmolL−1, respectively. Ca2+, Mg2+, and cysteine substantially increased the activity of the enzyme but chelating agents, heavy metals (Cd2+, Pb2+, Cu2+, Zn2+, etc.), NADPH, and ADP had significant inhibitory effects. This glutathione reductase can be used to study the adaptation
and mechanism of catalysis of psychrophilic enzymes, and it has a high potential as an environmental biochemical indicator
under extreme conditions.