The phosphate-binding protein of Escherichia coli

Abstract

1. 1. Escherichia coli contains a phosphate-binding protein, in amounts exceeding 2 · 10 4 molecules per cell. Over 80% of this protein is released by osmotic shock. 2. 2. The phosphate-binding protein has been purified and found to have a molecular weight of 42 000. There is no evidence of subunits or aggregation. 3. 3. Each molecule of the protein binds one molecule of phosphate. This activity is inhibited by a specific rabbit antiserum. 4. 4. Cold-shocked E. coli lose the ability to transport phosphate. The purified binding protein when added to cold-shocked E. coli stimulates phosphate uptake. This effect is abolished by the specific antiserum. 5. 5. The phosphate-binding protein also stimulates phosphate uptake in a mutant of E. coli with impaired phosphate transport and which also lacks this protein. It does not have any effect on phosphate uptake in another mutant which has the binding protein but is deficient in phosphate uptake through another lesion.