The photo-assimilation of acetate by Rhodospirillum rubrum

Sedimentation and diffu8ion.Measurements of the sedimentation velocity of purified inhibitor AA, at five 8 min.intervals, showed a single sym- metrical boundary.This single component in a solution containing 1 g./100 ml. had S20,w 2 3s and D20,, 9 03 x 10-7 cm.2/sec.These sedimentation and diffusion coefficients, together with an as- sumed partial specific volume of 0 75 ml./g., indi- cate that purified inhibitor AA has mol.wt. 24 000.I8oelectric point.Determinations of the solubility of the purified inhibitor in 0 IM-sodium acetate buffers in the range pH 3 90-455 indicated an isoelectric point of 4-2.Amino acid content.The tyrosine and methionine contents of an hydrolysate of purified inhibitor AA were 1*9 and 1D0 g. respectively/100 g. of inhibitor hydrolysed.The complete absence of tryptophan from purified inhibitor AA is of special interest as Kunitz's crystalline soya-bean trypsin inhibitor is apparently the only pure trypsin inhibitor that contains significant quantities of tryptophan (Laskowski & Laskowski, 1954).The non-identity of purified inhibitor A with the crystalline soya- bean trypsin inhibitor of Kunitz, which was established by the distinctly different behaviour on a DEAE-cellulose colunm (Birk, 1961b), is further substantiated by the present work.SUMMARY 1.Further purification of an acetone-insoluble trypsin inhibitor on a carboxymethylcellulose column and its separation from a highly active amylase has been described.2. The purity of the inhibitor has been established by rechromatography on carboxymethyland diethylaminoethyl-cellulose and by ultracentrifugal analysis.3. The molecular weight of the pure inhibitor was determined as 24 000 and its isoelectric point was pH 4-2.4. The non-identity of the pure inhibitor with the crystalline soya-bean trypsin inhibitor has been further substantiated by its higher specific activity (13-fold) against chymotrypsin and by the absence of tryptophan.