[Secretion of periplasmic PhoA protein during its supersynthesis into the medium using outer membrane vesicles. Features of chemical composition of the vesicles and membranes of Escherichia coli secreting cells].

E. coli K12802 cells transformed by multicopy plasmid with phoA gene acquire the ability to oversynthesize alkaline phosphatase, secrete it into the cultural medium, and accumulate the precursor of this enzyme. The dynamics of enzyme production and secretion as well as cytomorphological changes revealed the existence of a mechanism of selective enzyme secretion into the medium. It is characterized by a decrease of enzyme specific activity in periplasm and its increase in cultural medium, appearance of numerous local zones of adhesion of cytoplasmic and outer membranes, formation of large extracellular outer membrane vesicles containing PhoA protein on the cell poles, and their release into the medium. We isolated the vesicles and found that they contain PhoA (in dominating quantity), several other periplasmic proteins, and matrix proteins of outer membranes. By their phospholipid and protein composition, they correspond to the fraction of outer membranes which have the largest density and sedimentation rate and, apparently, contain no lipoprotein.