A widely distributed enzyme which transfers part of a 1,4-glucosan chain from a 4- to a 6-position in polysaccharides. Isoln from potatoes: Barker et al., J. Chem. Soc. 1949, 1705. Crystallization: Gilbert, Patrick, Biochem. J. 51, 181 (1952). Improved isoln procedure: Griffen, Wu, Biochemistry 7, 3063 (1968). Although Q-enzyme is unstable in aq soln, it can be stored for long periods without appreciable loss in activity when it is freeze-dried. Review: Barker, Bourne, Q. Rev. Chem. Soc. 7, 65-68 (1953); Dixon, Webb, Enzymes (Academic Press, New York, 1958) passim.