Isolation and study of functional membrane proteins Present status and future prospects

The purpose of this review letter is to summarize recent attempts to label and isolate membrane proteins, in particular, substrate transporters, and also several drug receptors and enzymes.It is assumed that the transport or receptor system has already been studied with respect to substrate specificity, inhibitors, kinetics etc., before efforts are begun to isolate the proteins involved in the activity.Attempts to isolate these specific proteins may be divided into two types:1) The protein is specifically labelled in situ, solubilized, and then purified.2) Alternatively, the membrane is solubilized, and the protein identified and purified subsequently. In situ labelling2.1.The pgalactoside perrnease in E. coliThe theoretical and practical aspects of active site labelling of purified soluble proteins have been discussed [l-3] .One major point to be emphasized here