aDepartment of Biochemistry, University of Wisconsin, Madison, WI 53706, USA;bDepartment of Chemistry, and Department of Biochemistry and Biophysics, Texas A&;M University, College Station, TX 77843, USA
Abstract:
The direct transfer of metabolites from one protein to another in a biochemical pathway or between one active site and another within a single enzyme has been described as substrate channeling. The first structural visualization of such a phenomenon was provided by the X-ray crystallographic analysis of tryptophan synthase, in which a tunnel of approximately 25 Å in length was observed. The recently determined three-dimensional structure of carbamoyl phosphate synthetase sets a new long distance record in that the three active sites are separated by nearly 100 Å.