Hexokinase binding to polypropylene test tubes: Artifactural activity losses from protein binding to disposable plastics

Abstract

In the course of our studies with rat brain hexokinase (ATP: d-hexose 6-phosphotransferase, EC 2.7.1.1), we have frequently used disposable polypropylene centrifuge tubes. As long as relatively crude systems with substantial amounts of extraneous protein were used, no difficulties were encountered. However, with more purified preparations, substantial apparent activity losses were incurred. Investigation of the situation disclosed that the reason for these apparent losses was adsorption of the hexokinase to polypropylene vessels, an unusual adsorption that appeared to be particularly effective at the air-water interface. Subsequently, we found similar effects with other enzymes. Although binding of some proteins, such as ribonuclease (1,2), to glassware has been reported, we do not know of a similar phenomenon being described for plastic ware. The increased use of disposable plastic laboratory ware necessitates an awareness of this potential problem. We present here the results of our study of the adsorption of hexokinase to polypropylene.