3-Mercaptopyruvate sulphurtransferase from rat erythrocytes

3-Mercaptopyruvate sulphurtransferase (EC 2.8.1.2) was isolated from rat erythrocytes and purified to apparent homogeneity. On disc electrophoresis and isoelectric focusing the enzyme showed microheterogeneity; four enzymatically active microzones of isoelectric points ranging from 5.5 to 7.5, resistant to neuraminidase treatment were detected. The molecular mass of the enzyme determined by the density gradient ultracentrifugation, gel filtration and sodium dodecyl sulphate polyacrylamide-gel electrophoresis was found to be about 36,000. The enzyme is a sialoprotein composed of 219 amino acid and 38 carbohydrate residues. Kinetic parameters of 3-mercaptopyruvate sulphurtransferase from rat erythrocytes were similar to those found for the enzymes isolated from rat liver and Escherichia coli. The purified enzyme was very unstable; spontaneous inactivation could be partly prevented by glycerol (1:5, v/v).