Glutathione S-Transferases From Antarctic Fish

Abstract

Glutathione S-transferase activity was found in liver homogenates from Antarctic fish species Dissostichus mawsoni and Pagothenia borchgrevinki. Activities measured with 1-chloro-2,4-dinitrobenzene were 11.2 µmol min-1 mg-1 and 16.7 µmol min-1 mg-1 respectively. Little or no activity was detected with p-nitrobenzyl chloride or 3,4-dichlorol-nitrobeuzene. Glutathione was found in the livers of Antarctic fish in millimolar quantities. The partial purification of glutahione S-transferases from D mawsoni is described. The effects of temperature and pH on the spontaneous and enzyme catalysed reaction are described. The spontaneous reaction rate being characterized by the activation parameters (A = 26.33+0.7 , ∆H# = 50.71+1.67 KJ mol-1) and the sulphdryl proton ionization parameters (∆H = 31.4+2.5 KJ mol-1, ∆S = 72+8 J mol-1 K-1). The effects of pH on the glutathione S-transferase from G mellonella are examined. The reduction in catalytic action at high pH being due to ionizations associated with glutathione binding (pKa 8.6+0.2, 9.2+0.2). The effects of temperature are discussed in both thermodynamic terms and in the ability to enhanue the spontaneous reaction. Isoenzymes from rat, G mellonella and D mawsoni are charauterized. Rate enhancement factors were within a ten fold range, suggesting Antarctic fish have an effective detoxication system.