[34] Preparation of low-molecular -weight forms of rabbit muscle protein phosphatase

Publisher Summary The low-molecular-weight form of phosphorylase phosphatase proved readily amenable to purification by a combination of ion-exchange chromatography and gel filtration, and was first purified from rabbit liver. The availability of the purified enzyme allowed the initial characterization of phosphorylase phosphatase as an enzyme of broad specificity. In addition, two such enzymes were isolated from rabbit liver, one with a high specific activity toward phosphorylase, and one with a lower specific activity to this substrate. The examination of the 35K phosphatases from rabbit muscle also led to the identification of two such enzymes, which are designated phosphatase C-I and C-II for convenience. It was proposed that the ∼35K low-molecular-weight phosphatases were the catalytic subunits of larger holoenzymes, based on the dissociation of phosphorylase phosphatase from higher molecular weight forms, and the existence of heat-stable protein inhibitors which formed larger complexes in association with the 35K enzyme. This hypothesis is now generally accepted, and is applicable to both the type-1 and type-2A phosphatases.