Proline isomerization and the slow folding reactions of the alpha subunit of tryptophan synthase from Escherichia coli
Hurle, M.R.; Matthews, C.R.
Biochimica et Biophysica Acta 913(2): 179-184
ISSN/ISBN: 0006-3002 PMID: 3297161 Accession: 006199535
Previous studied on the refolding of the .alpha. subunit of tryptophan synthase from Escherichia coli assigned two slow refolding phases to rate-limiting isomerizations of two 'essential' proline residues, one in each of the two domains of the protein (Matthews, C.R., Crisanti, M.M., Manz, J.T. and Gepner, G.L. (1983) Biochemistry 22, 1445-1452). The double-jump experiment (Brandts, J.F., Halvorson, H.R. and Brennan, M. (1975) Biochemistry 14, 4953-4963) was used to further investigate this phenomenon. The reaction assigned to the carboxyl domain is consistent with the proline isomerization hypothesis. The amino domain process is more rapid than expected for proline isomerization and may reflect another type of slow folding reaction. The results permit a further refinement of the folding model for the .alpha. subunit and demonstrate the existence of a third unfolded species whose folding is not limited by either of these two reactions.