(1) Isopentenyl pyrophosphate isomerase was isolated from Bakers yeast (specific activity 6.5 nmol/min/mg).'Enzyme purified in this manner was essentially free of prenyl transferase activity and was assayed as described. s A unit of enzyme activity is defined here as 1 nmol/min.(2)(a) Shah, DH; Cleland, WW; Porter, J. WJ Biol. Chem. 1965, 240, 1946.(b) Rose, IA" The Enzymes", 3rd ed.; Boyer, PD, Ed.; Academic Press: New York, 1970; Vol. ...