ε-N-Dimethyllysine in Amoeba Actin

Abstract

AMOEBA actin, a protein that shares many of the chemical, physical, and ultrastructural properties of muscle actin, has recently been isolated from Acanthamoeba castellanii^1,2. The final steps in the purification procedure are the sedimentation of polymerized amoeba F-actin, its depolymerization by prolonged dialysis against a solution of ATP, and separation by molecular filtration on ‘Sephadex G-200’ of a minor excluded fraction and a major included fraction (amoeba G-actin). The product is monodisperse as judged by sedimentation equilibrium centrifugation in 5 M guanidine¹ and has a molecular weight of about 39,500. Polyacrylamide gel electrophoresis at pH. 9.5 in 8.5 M urea of the reduced, carboxymethylated protein shows one major band that accounts for more than 90 per cent of the stainable protein. The amino-acid composition of amoeba actin was found to be very similar to that of other act ins including approximately 1 mole of the rare amino-acid 3-methylhistidine (3-MH) per mole of protein¹. In addition, an unidentified component was detected which had the same elution time as ε-N-methyllysine in the chromatographic system used¹ which does not separate monomethyllysine from dimethyllysine.