Metabolic and genetic control of isoenzyme spectrum of alkaline phosphatase inEscherichia coli

Abstract

Three proteins possessing alkaline phosphatase activity were detected in a fraction of periplasmic material of Escherichia coli K-10 and its mutants with constitutive synthesis of alkaline phosphatase. They also showed acid phosphatase, pyrophosphatase and ATPase activities. Through the use of phosphatase-negative mutants it was shown that these proteins were the products of a single structural gene and therefore represented alkaline phosphatase isozymes. The numbers of enzyme isoforms and possibly the spectrum of their phosphohydrolase activities were controlled by exogenous orthophosphate and depended on the integrity of regulator genes for alkaline phosphatase.

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

“…We have also shown previously (17) that the three forms from the derepressed celLs are synthesized independently of Pi in mutants with constitutive biosynthesis of alkaline phosphatase.…”

“…Analytical methods for determining enzyme activity. Phosphohydrolase activity was determined as described previously (17). Alkaline phosphatase and acid phosphatase activities were determined by the rate of hydrolysis of p-nitrophenylphosphate in incubation medium containing: for alkaline phosphatase-100 mM Tris-hydrochloride (pH 8.5), 10 mM MgC92, and 8 mM p-nitrophenylphosphate; for acid phosphatase-160 mM acetate buffer (pH 4.0) and 12 mM pnitrophenylphosphate.…”

“…Previously, we studied the influence of Pi (a specific regulator of biosynthesis of this enzyme) and mutations in regulatory genes of alkaline phosphatase on the multiple forms. It has been established that the number of isoforms of alkaline phosphatase depends on the state of the regulatory system of its biosynthesis (11,17). Under conditions of repression of alkaline phosphatase (when Pi is present in the medium) in the wild-type strain of E. coli K-10, only one form of enzyme isozyme prevails.…”

“…Under conditions of phosphorus starvation, the amounts of the two other forms increase. In mutants with constitutive synthesis of alkaline phosphatase, all three isoforms are synthesized constitutively irrespective of the availability of Pi in the medium (11,17). Independent of the growth conditions and the nature of the strain, all of the isoforms were shown to have broad substrate specificity and to hydrolyze not only para-nitrophenylphosphate, but also ATP, PPi, and other substrates.…”

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

“…This process includes the cleavage of N-terminal Arg by modifying proteinase (iap gene product) and dimerization of subunits. Three enzyme isoforms are formed during modification: a dimer of identical subunits with uncleaved Arg residues (isoform I); a heterodimer with Arg absent in one subunit only (isoform II); and a dimer with both subunits lacking the N-terminal Arg (isoform III) [43,44]. The ratio of these isoforms depends on cultivation conditions and the level of enzyme expression [45,46].…”