<scp>l</scp>‐Phenylalanyl‐tRNA Synthetase of <i>Escherichia coli</i> K‐10

Abstract

The molecular weight of l ‐phenylalanyl‐tRNA synthetase was redetermined. A new value of 267 000 was obtained by high‐speed analytical ultracentrifugation and Sephadex G‐200 gel chromatography. The value is in contrast to the molecular weight of 180000 determined previously From the molecular weight 267000 and the sedimentation coefficient s 20,w = 8.6 S the ratio f/f 0 = 1.67 was calculated. The magnitude of f/f 0 is in accord with the molecular weight 183000 obtained from sucrose gradient centrifugation. The results indicate that the enzyme is highly hydrated and/or assumes the shape of a rod or a disc. The subunit composition was reinvestigated by sodium dodecylsulfate gel electrophoresis, guanidinium chloride gel filtration and by reactivation experiments of pH‐2 inactivated enzyme. The results are consistent with a subunit structure of the α 2 β 2 type. Molecular weights of the subunits are 39000 and 94000, respectively.