Degradation of abnormal proteins in Escherichia coli. Differential proteolysis in vitro of E. coli alkaline phosphatase cyanogen-bromide-cleavage products.

Escherichia coli alkaline phosphatase has been purified and modified by either carboxymethylation or treatment with cyanogen bromide (CNBr). Only the CNBr-treated protein was degradable in an E. coli cell extract. Separation of the CNBr cleavage products by gel filtration in non-denaturing conditions gave rise to a number of oligomeric complexes, of which only those of molecular weight less than approximately 29000 were degradable in E. coli cell-free extracts. Carboxymethylation of the non-degradable complexes (greater than 29000 molecular weight) resulted in the formation of some complexes of less than 29000 molecular weight: such newly formed complexes were degradable by E. coli cell-free extracts. It is suggested that E. coli cell-free extracts may contain a protease/peptidase system which is active against peptide complexes below 29000 molecular weight, but inactive against peptide oligomers of greater molecular weight.