Baohuai Wang

Microcalorimetric study on the interaction of F-actin with myosin and its proteolytic fragments

Abstract The heat effect produced in the interaction of rabbit muscle F-actin with myosin and its proteolytic fragments (HMM, S 1 ) was measured with an MS-80 Calvet microcalorimeter (Setaram, France). An improved reaction cell of the microcalorimeter was used. There were three thermokinetic peaks in the measured curve of the interaction of myosin with F-actin in the absence of ATP, which were exothermic, endothermic and exothermic in order of appearance. When ATP was added to F-actin before mixing with myosin, the curve remained similar in feature to that in the absence of ATP. But the first peak (exothermic) became smaller and the second and third peaks became larger. There was only one exothermic peak in the measured curve of the interaction between S 1 and F-action. But ATP caused big changes in the curve of their interaction. With addition of ATP to F-action solution before it was mixed with S 1 , there were four thermokinetic peaks in the curve which were endothermic, exothermic, endothermic, and exothermic in order of appearance. The measured curves of interaction between HMM and F-actin in the presence and absence of ATP were quite similar to that of interaction between S 1 and F-action.

Interactions of calf thymus DNA with short chain oligoamides

In order to detect the biological activity of new synthetic short chain oligoamides, the present work gives the results of studies on the interaction between calf thymus DNA and short chain oligoamides: PyPyPy-g-Dp (ligand 1) and PyPyPyPy-g-Dp (ligand 2). In the circular dichroism (CD) spectra of the mixing solution of DNA with ligands a specific peak appears in the region of 300‐380 nm wavelength, which indicates that both ligands 1 and 2 can bind calf thymus DNA specifically. 1 H NMR spectra show that aromatic ring protons of ligand 1 appear as an obvious down-field shift, while those protons in ligand 2 disappear since ligand 2 owns a higher binding affinity with DNA than that of ligand 1. Investigations of DNA transition by differential scanning calorimetry (DSC) reveal that DNA melting temperature rises due to binding with ligands, and that ligand 2 alters the DNA transition process more significantly. At the same time, the molar binding enthalpies of ligands with DNA are measured at 293 K. The difference between the binding affinity of ligand 1 and 2 with DNA implies that increasing the number of N-methylpyrrole increases both the binding site size and the binding affinity. # 2002 Elsevier Science B.V. All rights reserved.

Urease conformational change induced by transplatin: A comparison on the interaction of urease with transplatin and cisplatin

Abstract The interaction between transplatin and urease was studied by microcalorimetry, DSC, circular dichroism (CD) spectrum and fluorescence spectrum. Transplatin can render urease inactive as is indicated by the experimental results of microcalorimetry. Thermal denaturation experiments of urease by DSC show that transplatin generally reduces urease thermal stability since urease T m decreases dramatically. From the features of urease CD and fluorescence spectra, transplatin leads to urease conformational change at lower concentrations than in case of cisplatin. The interaction of transplatin with urease is stronger than that of cisplatin and the binding site of urease with transplatin may be different from that with cisplatin.

Microcalorimetric investigations of K+- and Mg2+-induced polymerization of actin at temperatures from 293.15 K to 310.15 K

Microcalorimetric measurements of the polymerization of actin in the presence of 100 mM KCl and 2 mM MgCl2were carried out with a Calvet MS-80 microcalorimeter at temperatures from 293.15 to 310.15 K. It was observed that the polymerization of actin was endothermic and the enthalpy change for actin polymerization was temperature-dependent. The enthalpy change ΔHowas fitted to ΔHo(kJ mol-1)=434.0-1.16 (T/K) and the change in heat capacity ΔCpocalculated from ΔHowas -1.16 kJ (mol K)-1in the above range of temperatures. The direct calorimetry results showed that the enthalpy and entropy change for actin polymerization could not be obtained from measurements of the critical concentration and the only way to assess the enthalpy change for the polymerization of actin and similar reactions lies in the use of calorimetry.

Thermodynamic analysis of K+- and Mg2+-induced polymerization of actin at the temperature of 298.15 K

Abstract Polymerization of actin was investigated by a microcalorimetric method at 298.15 K. The calorimetric curves showed that polymerization of actin in the presence of Mg 2+ at the concentration range 1.00–6.00 mM was an exothermic process. There was only one exothermic peak in the thermal curves under each condition. The average molar enthalpy change of actin polymerization was −0.703 kJ mol −1 . It was still exothermic in the presence of K + when the concentration was in the range 25.0–200.0 mM. The average molar enthalpy change of polymerization was −3.03 kJ mol −1 . However, the calorimetric curves contained only one exothermic peak when the K + concentration was lower, in the range 25.0–75.0 mM; there were two peaks, first exothermic and second endothermic, in the calorimetric curves as the K + concentration was higher, in the range 100.0–200.0 mM. The result not only indicated that calorimetric curves of actin polymerization changed with different concentration of K + but also showed that there were some differences between K + - and Mg 2+ -induced polymerization of actin in the presence of 0.1 mM CaCl 2 and 0.2 mM ATP. The ΔG 0 of actin polymerization in each condition was also assayed at 298.15 K and ΔS 0 in the corresponding condition were consequently evaluated from the energy-entropy relation at constant temperature and pressure.