A coupled optical enzyme assay for phosphopentomutase

Published assays for phosphopentomutase activity are based on acid lability differences between ribose 1-phosphate and ribose 5-phosphate. The present work describes a new method in which the isomerization of ribose 5-phosphate to ribose 1-phosphate is followed spectrophotometrically at 265 nm by coupling it with the following two-stage enzymatic conversion: ribose 1-phosphate + adenine ⇌ phosphate + adenosine (adenosine phosphorylase); adenosine + H 2O → inosine + NH 3 (adenosine deaminase). The method has been used to show some properties of Escherichia coli phosphopentomutase.