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E3 Immunity Substance

1974; Elsevier BV; Volume: 249; Issue: 2 Linguagem: Inglês

10.1016/s0021-9258(19)43050-0

1083-351X

J. Sidikaro, Michio Nomura,

Toxin Mechanisms and Immunotoxins

Abstract Colicin (E3) inactivates ribosomes both in vivo and in vitro by causing a specific cleavage of 16 S ribosomal RNA. A protein which prevents the E3-induced in vitro ribosome inactivation has been isolated from E3-colicinogenic cells and purified to a homogeneous state as judged by polyacrylamide gel electrophoresis at pH 8.7 and sodium dodecyl sulfate polyacrylamide gel electrophoresis at pH 7.1. The purified protein (called E3 immunity substance) has no detectable phosphorus or carbohydrate. It is a very acidic protein and its molecular weight is about 9500. The amino acid compositions of the protein and its tryptic peptides were determined. There was good correspondence between the amino acid composition calculated from the sum of amino acid residues in the tryptic peptides and the amino acid composition of the whole protein, confirming the homogeneity of the purified protein preparations. The immunity substance was found only in extracts from cells carrying E3-colicinogenic factor (Col factor), but not in extracts from cells carrying other colicinogenic factors, suggesting that either the structural gene for the immunity substance is located on the Col factor or the production of immunity substance is controlled by a gene on the factor. This finding also suggests that the isolated immunity substance is responsible for immunity of E3-colicinogenic cells in vivo. Direct interaction of immunity substance with colicin in the absence of ribosomes has been demonstrated by experiments in which the immunity substance inhibited the reaction of anti-E3 antibodies with colicin E3. However, immunity substance does not irreversibly inactivate colicin E3. Other experiments suggest that the interaction of with immunity substance shows a 1:1 molar stoichiometry; 1 molecule of immunity substance neutralizes 1 molecule of E3. This could account for the immunity breakdown of colicinogenic cells by large excess of homologous colicins observed in in vivo experiments.