SUMMARY: Three methods for the purification of delta haemolysin were compared (Kantor , 1972; Kreger , 1971; Heatley, 1971). The products of these purifications from the culture supernatant of strain RN25 were compared by electrophoresis, amino acid analysis, amino-terminal sequence analysis and thin-layer chromatography. The method of Heatley (1971) was found to be superior in terms of recovery and purity of the product. Delta haemolysin prepared by the method of Kreger (1971) could not be sequenced successfully prior to treatment aimed at the removal of the -formyl group at the amino-terminus. Delta haemolysin appears to exist in two distinct molecular forms, one with -formylmethionine and the other with un-formylated methionine in the amino-terminal position. The former polypeptide species is purified preferentially by the method of Kreger (1971). Thin-layer chromatography of the products of each method of purification revealed that they were all heterogeneous, although the major component from the product of the method of Heatley (1971) represented not less than 70% of the product.


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