Studies on the mechanism of action of the histone kinase dependent on adenosine 3′,5′‐monophosphate

Abstract

The transient phase of histone HI phosphorylation was studied by the quenched-flow method. A 'minimal' kinetic scheme of the above process was proposed. A formal kinetic analysis was given to a four-step mechanism of the reaction. Computer simulation of the transient-phase kinetics of H I phosphorylation and the steady-state kinetics of phosphate transfer from the enzyme phosphoform to histone permitted us to estimate all kinetic constants of the proposed mechanism.Of late the problems related to protein phosphorylation have been given ever increasing attention and thorough consideration [I]. Knowledge of the entire mechanism of the protein kinase action is indispensable for elucidating a great many important aspects of protein phosphorylation [2]. A number of serious obstacles, such as difficulties in isolation, rather complex allosteric regulation and kinetic mechanism, have so far hindered the construction of a general scheme of catalysis by this class of enzymes.In this respect structural investigations are of obvious interest [3], studies on the mechanism of enzyme activation [4] and the mechanism of interaction of individual subunits [5,6], as well as NMR and steady-state kinetics experiments [7]. However, great possibilities, suggested by the analysis of the transient-phase kinetics of the reaction catalysed by protein kinase, remain unused. This approach was successfully applied in recent studies for a number of kinases [8 -101 and allowed the estimation of constants for the elementary stages of the phosphorylation processes of various lowmolecular-weight substrates.In this study cyclic-AMP-dependent pig brain protein kinase specific to lysine-rich histones, in particular H 1 , was used as the object of investigation [I 11. In the previous studies of this series [12,13], the ping-pong bi-hi mechanism for the kinase under study was established, functionally important groups of the enzyme active site were identified, and the intermediate of the phosphotransferase reaction, namely the phosphoform of the enzyme catalytic subunit, was isolated and characterized. The analysis of the transient phase of the reaction by the quenched-flow technique enabled us to determine all the constants for the elementary stages of the process of formation of the phosphoenzyme intermediate and its hydrolysis. This is the fourth paper of a series, which started with [12,13.21].Ahhrevicrtiom. H1, histone HI : C, catalytic subunit of histone kinasc; Lnzyr?zc~. Cyclic-AMP-dependent histone kinase or ATP:protein R, regulatory subunit of histone kinase. phosphotransferase (EC 2.7.1.37).Here we aimed at analysing the transient phase of thc entire reaction, including both the stage of formation of the enzyme phosphoform and the stage of phosphate transfer from the latter to the protein substrate, i.e. histone HI. MATERIALS A N D METHODS Matcria1.rPreparations of the homogeneous catalytic subunit of the pig brain CAMP-dependent histone kinase were obtained by the technique described [15].The "P-labeled phosphoform of the enzyme catalyt...

Protein Kinase A: Regulation and Receptor‐Mediated Delivery of Antisense Oligonucleotides and Cytotoxic Drugs

“…12 In the next series of experiments, we studied the kinetic mechanism of the phosphotransferase reaction catalyzed by cAMP-dependent protein kinase from pig brain. [13][14][15] Based on the two feasible kinetic mechanisms of this reaction-namely, the random bi-bi and ping-pong mechanisms-we provided a rationale for the ping-pong mechanism, which includes the intermediate formation of the phosphoryl-enzyme complex (FIG. 3).…”