Phosphoglucose isomerase from Escherischia coli K10: Purification, properties and formation under aerobic and anaerobic condition

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Abstract
Phosphoglucose isomerase has been purified from crude extracts of Escherichia coli K10. Two forms of the enzyme were separated during the purification procedure. The major species comprises more than 90% of the enzyme activity, has an apparent molecular weight of about 125,000 and consists of two 59,000 molecular weight subunits; the minor species has an apparent size of 230,000 and consists of (possibly four) subunits of 59,000 molecular weight. Both enzyme forms have the same N-terminal amino acid, the same pH optimum of reaction and the same kinetic constants for the substrate fructose-6-phosphate and the inhibitor 6-phosphogluconate. They differ in that the minor species has half the specific enzyme activity compared to the major one and that its subunit polypeptide carries a higher electronegative charge. Since they are both coded by the pgi gene and since they show full immunological identity it seems that the minor species is a dimer of the major enzyme form and that dimerisation is caused by subunit modification. No physiological role could be found for the existence of the two forms. — Formation of phosphoglucose isomerase is under respiratory control: under anaerobiosis the enzyme (both species) is derepressed parallely with other glycolytic enzymes.