Hybrid enzyme of liver phosphorylase and phosphorylase I.

A hybrid enzyme (LI) of liver phosphorylase [EC 2.4.1.1.] (L) and phosphorylase I, which is mainly located in brain, was isolated and its enzymatic and immunological properties were examined. The following results were obtained: (1) AMP stimulated the b forms of the hybrid (LIb), I(Ib), and L(Lb); (2) in the presence of AMP, SO42- stimulated Lb more than LIb and inhibited Ib; (3) in the absence of AMP, SO42- stimulated all three isozymes in the order: Ibeta less than LI less than Lbeta; (4) on conversion to the a forms, the activities of L, LI, and I increased 35.5-fold, 3-fold, and 1.2-fold, respectively; (5) the relative inhibition potencies of anti-Lb antibody with LIa and LIb were 63% and 4%, respectively of that with La, and those of anti-Ib antibody with LIa and LIb were 42% and 88%, respectively of that with Ia. Since the ratios of the specific activities of purified La and Ia and of Lbeta and Ibeta are 70: 82 and 2 : 70, respectively (Schliselfeld, 1973), the present findings suggest a 1 : 1 association of I and L subunits in the hybrid molecule.