Metabolic and genetic control of isoenzyme spectrum of alkaline phosphatase in Escherichia coli

The change in membrane phospholipid composition influences protein secretion and cell envelope biogenesis in Escherichia coli

Secretion of periplasmic alkaline phosphatase (PhoA) encoded by the gene constituent of plasmids and the peculiar properties of cell envelope biogenesis in Escherichia coli strains with controlled synthesis of individual membrane phospholipids have been studied. Alkaline phosphatase secretion across the cytoplasmic membrane declines, while secretion into the culture medium intensifies under changed metabolism. The composition of anionic membrane phospholipids changes due to inactivation of the pgsA gene or regulation of its expression by environmental factor, as well as in the absence of the pssA gene which is responsible for the synthesis of the precursor for zwitter-ionic phospholipid — phosphatidylethanolamine. This correlates with intensified secretion of exopolysaccharides and lower content of lipopolysaccharide and lipoprotein which are responsible for barrier properties of the outer membrane. The results suggest a possible coupling of protein secretion with biogenesis of cell envelope components at a level of phospholipid metabolism.

Multiple forms of alkaline phosphatase from Escherichia coli cells with repressed and derepressed biosynthesis of the enzyme

Isolation of multiple forms of alkaline phosphatase from Escherichia coli cells with repressed and derepressed biosynthesis of the enzyme is reported. Three enzyme forms were isolated from cells with derepressed synthesis, and one form was isolated from cells with repressed enzyme synthesis. The multiple enzyme forms did not differ in pH optimum, thermostability, or the degree of inhibition with orthophosphate; however, they did differ in the relative rate of hydrolysis of different substrates. The addition of substrates to the cells during enzyme derepression resulted in changes of the ratio of the multiple forms.