Isolation and characterization of octopus hepatopancreatic glutathione S-transferase. Comparison of digestive gland enzyme with lens S-crystallin.

Glutathione S-transferase from Octopus vulgaris hepatopancreas was purified to apparent homogeneity by single glutathione-Sepharose-4B affinity chromatography with overall yield 46% and purification 249-fold. The enzyme was a homodimer with subunit M(r) 24,000, which was smaller than that of the octopus lens S-crystallin (M(r) 27,000) with glutathione-S-transferase-like structure. Both proteins showed substrate specificities similar to alpha/pi-type isozyme of glutathione S-transferase. Under native conditions, both proteins exhibited multiple forms upon polyacrylamide gel electrophoresis or isoelectric focusing, albeit with distinct mobilities; however, only one kind of N-terminal amino acid sequence was determined for the multiple forms of each protein. The hepatopancreatic GST, with pI value 6.6-7.3, dissociated into two monomers in an acidic or alkaline environment. Two amino acid residues, with pKa values 5.69 +/- 0.14 and 9.03 +/- 0.11 were involved in the subunit interactions of the hepatopancreatic enzyme.