genzyme genzyme biochemicals lts maidstone england genzyme corp boston mass u s a it has been described by n lambert and r b freedman 1983 biochem j 213 225 234 this type of enzyme seems to occur in every eukaryotic tissue which synthesises a secreted protein the most easily obtainable tissue type is bovine liver pdi this may be isolated as follows 500g of diced bovine liver is washed with physiological saline and extracted at neutral ph with phosphate buffer which contains 1 triton this gives an enzyme extract which is then concentrated and purified by procedures involving heat treatment ammonium sulphate precipitation ion exchange chromatography dialysis and finally lyophilization see the paper by lambert and freedman for fuller details a purer enzyme may be prepared by genetic engineering i e using cloned dna in a suitable culture for use it is generally necessary to add a very small amount of a low molecular weight thiol as a cofactor the concentration need only be of the order of micromolar an example of a suitable thiol which is readily available and is acceptable for treatment of fabrics is dithiothreitol or more preferably reduced glutathione a suitable composition for use contains 0 01 to 1 0g preferably 0 03 to 0 3g of pdi and 1 to 1000 preferably 10 to 1000 micromoles of a.