Periplasmic Alkaline Phosphatase Activity and Abundance in Escherichia coli B23 and C29during Exponential and Stationary Phase

Abstract

Alkaline phosphatase (AP), encoded by pho A, is a periplasmic, homodimeric protein that is responsible for the hydrolysis of phosphate molecules from non-transportable organophosphates. Osmotic shock was employed to specifically isolate periplasmic proteins from E. coli C29 constitutive AP strain during exponential and stationary phase growth. Assays were performed for AP activity and abundance. Our findings confirm previously observed results that levels of AP specific activity and protein abundance increase in stationary phase compared to exponential phase growth. In addition, we examined AP trends in wild type E. coli B23 to determine whether the observed increase in AP activity and protein levels in E. coli C29 was the result of modified AP regulation at the transcriptional level. The rapid increase in AP specific activity at the onset of stationary phase in E.coli B23 suggests an induction event that may be due to pho A up regulation s mediated by phosphate starvation. σ -dependent global down-regulation of protein synthesis in stationary phase may contribute to higher AP specific activity due to a proportional increase of AP relative to the decreasing amount of cellular proteins.