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J Matkó

Publications and source records attributed to J Matkó.

41 records · Page 3Linked to original sources
PubMed1981

Rose bengal as a tool in studying the ligand binding of phosphorylase b.

The interaction of rose bengal (RB) with rabbit skeletal muscle phosphorylase b (1,4-alpha-D glucan: orthophosphate alpha-glucosyl-transferase, E.C. 2.4.1.1.) was studied by kinetic and absorption photometric methods. RB inhibited the phosphorylase b activity. Inhibition was strictly competitive with respect to substrate G-1-P and activator AMP with inhibition constants 2 x 10(-6) M and 2.2. x 10(-7) M, respectively. The association of the dye with the enzyme elicited a red shift in the spectrum of RB indicating an apolar binding site. According to difference absorption measurements, the enzyme binds two dye molecules per dimer in the presence and absence of both G-1-P and AMP. Binding constants determined from photometric titrations are consistent with those obtained from kinetic measurements. The present findings allow to carry out detailed kinetic investigations on the activator AMP and substrate G-1-P binding of phosphorylase b.

Adenosine Monophosphate↗
PubMed1980

Correlation between activity and dynamics of the protein matrix of phosphorylase b.

Quenching of the tryptophan fluorescence of phosphorylase b was studied by using iodide and acrylamide. Steady-state measurements indicated that all indole side chains were accessible to the nonionic quencher, although only 3 out of the total of 12 residues could be quenched by I-. From Stern--Volmer plots and the fluorescence lifetime data, it was concluded that the quenching was mainly of dynamic character. The value of the collisional quenching rate constant was found to be an order of magnitude less than that obtained in the case of fully exposed tryptophans. The relatively high activation energy, 30.9 kJ/mol, of the diffusion-controlled process and the value of the activation entropy suggest that the diffusion takes place in a fluctuating, structured medium. In spite of the application of sensitive fluorescent techniques, no gross conformational changes were found in the presence of acrylamide. However, the catalytic rate of the glycogen synthesis was decreased with the residual activity of the enzyme, proportional to the concentration of the probe. Binding of activator (AMP) and substrates (glucose 1-phosphate and glycogen) was found to be unaffected by acrylamide in concentrations applied (0--0.8 M). In a similar manner, activation enthalpy did not change in the presence of the quencher either. The complete reversibility of both activity inhibition and fluorescence quenching ruled out the irreversible denaturation of the enzyme or the covalent modification of any of the functional groups. We concluded that a model, suggesting the cross-correlation of activity and fluctuation, was consistent with the experimental findings.

Acrylamides↗
PubMedDate not supplied

Plasma-membrane-bound macromolecules are dynamically aggregated to form non-random codistribution patterns of selected functional elements. Do pattern recognition processes govern antigen presentation and intercellular interactions?

Molecular recognition processes between cell surface elements are discussed with special reference to cell surface pattern formation of membrane-bound integral proteins. The existence, as detected by flow cytometric resonance energy transfer (Appendix), and significance of cell surface patterns involving the interleukin-2 receptor, the T-cell receptor-CD3 system, the intercellular adhesion molecule ICAM-1, and the major histocompatibility complex class I and class II molecules in the plasma membrane of lymphocytes are described. The modulation of antigen presentation by transmembrane potential changes is discussed, and a general role of transmembrane potential changes, and therefore of ion channel activities, adduced as one of the major regulatory mechanisms of cell-cell communication. A general role in the mediation and regulation of intercellular interactions is suggested for cell-surface macromolecular patterns. The dynamic pattern of protein and lipid molecules in the plasma membrane is generated by the genetic code, but has a remarkable flexibility and may be one of the major instruments of accommodation and recognition processes at the cellular level.

Animals↗