Biochimica et Biophysica Acta 827 (1985) 23-29 23 Elsevier BBA 32081 Effects of acidic and basic macromolecules on the activity of protein phospbatase-1 Ferenc Erd6di, Csilla Csortos, Gy6rgy Bot and Pill Gergely * Institute of Medical Chemistry, University School of Medicine, Bern t& 18/B, Debrecen, H-4026 (Hungary) (Received June 26th, 1984) (Revised manuscript received September 21st, 1984) Key words: Protein phosphatase; Enzyme inhibitor; Polybrene; (Rabbit skeletal muscle) The dephosphorylation of phosphorylase a by the catalytic subunit of protein phosphatase-1 obtained from rabbit skeletal muscle is inhibited by heparin in a noncompetitive manner with respect to phosphorylase a (K i = 8 pg/ml). The inhibitory effect of heparin is also observed in the presence of effectors (e.g., glucose and AMP) modifying the dephosphorylation of phosphorylase a. Heat-stable protein inhibitors of protein phosphatase-1 can develop their inhibitory effect of the activity of protein phosphatase-1 even in the presence of heparin. The inhibitory effect of heparin and the heat-stable inhibitor-2 of phosphatase is additive. Polybrene, a heparin antagonist, prevented phosphatase-I from the inhibition caused by heparin or the inhibitors. Proteins with basic character, histone fractions (H1, H3) and protamine sulfate, can counteract with the inhibitory effect of heparin, but they cannot intercept the actions of inhibitor-1 or -2. Introduction Protein phosphatases (EC 3.1.3.-) catalyse the dephosphorylation of various phosphoproteins and for this reason considerable progress has been made in characterizing the nature of these en- zymes. Several types of phosphatase have been described which have been classified into two major groups [1,2]. This classification is based on sub- strate specificity and sensitivity to heat-stable in- hibitor proteins. Recently, it has been possible to isolate two low-molecular-weight protein phos- phatases from rabbit skeletal muscle [3-5], termed protein phosphatase-1 and -2. Protein phos- phatase-1 is inhibited by nanomolar concentra- tions of inhibitor-1 and inhibitor-2, whereas the type-2 phosphatases are insensitive to the protein inhibitors [6]. Most information about the control of activity of phosphatases has been provided by studies of * To whom correspondence should be addressed. dephosphorylation of phosphorylase a, a key en- zyme of glycogen metabolism. The activity of phosphatases are regulated by ligands, phos- phorylated and nonphosphorylated proteins, and other macromolecules. It is well known that ligand-induced conformational changes of phos- phorylase a can influence the rate of dephosphory- lation [7-9]. The activity of phosphatase is also inhibited by phosphorylase kinase and the regu- latory subunit of cyclic AMP-dependent protein kinase [10,11]. Macromolecules of acidic and basic nature can also modify the activity of protein phosphatases. In skeletal muscle, there are two heat-stable pro- teins, termed inhibitor-1 and -2 that are specific inhibitors of protein phosphatase-1. Inhibitor-1 is an effective inhibitor only after it has been phos- phorylated by cyclic AMP-dependent protein kinase [12]. Inhibitor-2 forms an inactive complex with the catalytic subunit of phosphatase-1 that is known as Mg-ATP-dependent phosphatase [13,3]. We have reported [14] that heparin inhibited the 0167-4838/85/$03.30 © 1985 Elsevier Science Publishers B.V.