Determination of binding parameters of cyclic AMP and its analogs to cyclic AMP-dependent protein kinase by the fluorescent probe method

The preparation of cyclic nucleotide-depleted regulatory subunits from type II adenosine 3':5'-monophosphate-dependent protein kinase by a nondenaturing method

A nondenaturing method for the preparation of R subunits from type II cyclic AMP-dependent protein kinase is described. The procedure is based on the exchange of cyclic AMP, which is tightly bound to the R subunit, for more weakly bound cyclic GMP, which can be removed by washing and dialysis. Less than 5% of the available cyclic nucleotide-binding sites of R subunit prepared by this method contained cyclic AMP and less than 3% contained cyclic GMP. The C-subunit contamination (mol of C/mol of R monomer) was approximately 0.2%. These levels of contamination did not affect the properties of the R subunit as judged by (a) the ability of the R subunit to inhibit the activity of the C subunit and (b) the rate of exchange of cAMP into R2 . etheno-cAMP. The advantages of our method are that the protein is not subjected to denaturing conditions and that large amounts of material can be processed relatively rapidly.

Studies on the mechanism of action of the histone kinase dependent on adenosine 3',5'-monophosphate. Investigation of protein-protein interaction by electron spin-resonance spectroscopy and stopped-flow methods

The interaction of the cAMP-dependent protein kinase catalytic subunit with its protein substrate, histone H1, was studied. The H1 molecule was specifically converted into the aminotyrosine-72 derivative. Fluorescent and spin labels were introduced into this residue. The changes in the ESR and fluorescence spectra of respective derivatives were observed upon the interaction of the latter with the catalytic subunit, thus enabling us to determine some kinetic and equilibrium parameters of this process. Stopped-flow investigation of the transient phase of the binding reaction indicates that the kinetic curve is described by a three-exponential function. The rate of protein-protein interaction is close to the rate of phosphate transfer from phosphoenzyme intermediate to protein substrate.

Nature of the riboflavin interaction with the immunoglobulin IgGGAR: analogue binding studies

The human immunoglobulin IgGGAR has been shown to bind riboflavin both in vivo and in vitro with a high binding constant [Farhangi & Osserman (1976), New Engl. J. Med. 294, 177-183; Chang et al. (1981b), Biochemistry 20, 2916-2921; Chang et al. (1981a), Biochemistry 20, 2922-2926] and, therefore, represents a natural human antibody hapten complex. In this study, the parts of the riboflavin molecule which are in intimate contact with the binding pocket have been identified, using a variety of riboflavin analogues. The binding constants of IgGGAR for these flavins were measured by fluorescence spectroscopy. The relative affinities indicate that the pyrimidine edge of the isoalloxazine interacts intimately with the combining site, particularly around N-3. The ribityl side chain and the dimethylbenzene edge of the flavin ring are not critical to the binding interaction and are probably exposed to solvent. Analogues of riboflavin with altered electronic structures have somewhat lowered affinities for IgGGAR, suggesting that the isoalloxazine ring forms stacking interactions. Comparison with other known flavin-binding proteins shows that IgGGAR binds riboflavin in a new way that is different from the sites in other proteins. The isoalloxazine ring binds similarly to the FMN-binding proteins; however, unlike virtually all the other proteins, the ribityl side chain is not essential to binding.

Studies on the mechanism of action of the histone kinase dependent on adenosine 3',5'-monophosphate. Interaction of ATP with the catalytic subunit of the pig-brain enzyme: application of the quenched-flow technique

A significant release of inorganic phosphate from ATP in the presence of the cAMP-dependent pig-brain histone kinase was detected. The high degree of homogeneity of the enzyme preparations used, identity of Michaelis constants (Km for ATP = 12 microM), the close values of cAMP activation constants (48 nM and 51 nM) for the phosphotransferase and ATPase activities, respectively, are all evidence that ATP decomposition is catalysed by the histone kinase under study. The ATPase activity observed supports the ping-pong bi-bi mechanism established earlier for the phosphotransferase reaction and can be regarded as due to decomposition of the phosphoryl enzyme. The transient and steady-state phases of the ATP hydrolysis were studied. The simplest reaction pathway can be described in terms of a three-step mechanism. The close values of the rate constant for the elementary stages of the ATPase reaction obtained in the nucleophile competition study and by computer simulation of the quenched-flow kinetics give further support for the mechanism proposed. The phosphoryl enzyme decomposition was shown to be a rate-limiting step under the experimental conditions used (pH 7.8-8.0).