Table of Contents
Metal-Based Drugs
Volume 2 (1995), Issue 3, Pages 127-136

A Spectroscopic Study on PtCl4(2) Binding to Rabbit Skeletal Muscle G-Actin

1State Key Laboratory of Coordination Chemistry, Coordination Chemistry Institute, Nanjing University, Nanjing 210008, China
2Inorganic Chemistry Department, School of Pharmaceutical Sciences, Beijing Medical University, Beijing 100083, China

Received 24 October 1994; Accepted 7 November 1994

Copyright © 1995 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


It was found that the binding of PtCl42 to G-actin and the consequent conformational changes are different with those for hard acids. It is a two-step process depending on molar ratio PtCl42/actin (R). In the first step, R less than 25, the PtCl42 ions are bound to sulfur-containing groups preferentially. These high-affinity sites determined by Scatchard approach are characterized by n1 = 30 with average binding constant K1=1.0×107M-1. The conformational changes are significant as characterized by N-(1-pyrenyl) maleimide(NPM) labeled fluorescence, intrinsic fluorescence and CD spectra. EPR spectroscopy of maleimide spin labeled(MSL) actin demonstrated that even PtCl42binding is limited to a very small fraction of high-affinity sites(R<1), it can bring about a pronounced change of conformation. In the range of R=25-40, high-affinity sites accessible are saturated. In the second step(R>40) , deep-buried binding sites turn out to be accessible as a result of the accumulated conformational changes. These new binding sites are estimated to be n2=26 with average binding constant K2=2.1×106M-1. Although in this step the quenching of intrinsic fluorescence goes on and the NPM-labled thiols moves to more hydrophilic environment, no change in α-helix content was found. These results suggested that with increasing in PtCl42 binding, the G-actin turns to an open and loose structure in a discontinuous mode.