The Arrhenius plot behaviour of rat liver 5′-nucleotidase in different lipid environments

The plasma membrane enzyme 5′-nucleotidase (EC 3.1.3.5) was prepared from rat liver as a complex with sphingomyelin or in detergent-solubilized forms. Each preparation exhibited a K_m and Arrhenius break temperature indistinguishable from that of 5′-nucleotidase in plasma membranes. Measurement of fatty acid profiles, cholesterol and phospholipid content however showed a very wide variation between these preparations. We conclude that the biphasic nature of the Arrhenius plot of 5′-nucleotidase may be a property of the enzyme rather than its lipid environment.