Purothionin (a lethal protein for brewer's yeast) obtained from wheat flour (Triticurm vulgare, Manitoba No. 3) was separated into two active fractions, A and B, by CM-cellulose column chromatography. The main component, purothionin A, was purified to a homogeneous state as shown by polyacrylamide gel disk electrophoresis and isoelectric focusing. The molecular weight of purothionin A was estimated by the sedimentation equilibrium method to be 11,300 in its native state, 5,500 in 6 M guanidine HCl and after its modification with succinic anhydride. Chemical studies including the determination of N- and C-terminal amino acid residues and amino acid sequence analyses using a combination of automatic Edman degradation and tryptic digestion of purothionin A revealed its dimeric structure composed of nonidentical and closely similar polypeptide chains. Two distinct polypeptides were isolated by DE-52 column chromatography after succinylation. Based on the amino acid composition of each polypeptide, it was possible to align all the tryptic peptides of purothionin A without any ambiguities, establishing the complete primary structures of the purothionin A subunits. The two polypeptides in purothionin A have very similar structures, differences occurring at the five positions enclosed by boxes.
No takes yet. Share an insight, caveat, or question.
OHTANI et al. (1977) studied this question.