SDS–PAGE analysis of purified recombinant wild type, 1–413 and 71–400 human CBS proteins. Twenty micrograms of each protein was run on 9% SDS-containing polyacrylamide gel and stained with Coomassie brilliant blue. Lanes: M, protein marker (precision plus molecular weight standard, Bio-Rad); 1, wild type CBS (5 μg); 2, 1–413 CBS (5 μg); 3, 71– 551 CBS (5 μg), respectively.