Exposure to various chemicals, either due to occupation or lifestyle, is considered to be a major contributing factor to tumour formation in man (Higginson, 1969; Doll & Peto, 1981). An important and prevalent class of potent carcinogenic compounds present in the environment is polycyclic aromatic hydrocarbons (PAHs), which are found in various petroleum and combustion products derived from heat and power generation and motor vehicle exhausts (Baum, 1978). Furthermore, since PAHs are generally formed by pyrolysis of organic matters such as tobacco smoking and certain procedures of food preparation, the PAH exposure to humans is extensive.

The intelligent design of new families of DNA-binding antitumour agents must await an understanding at the molecular level of the structure, dynamics and energetics of drug-DNA interactions on currently available systems. Recent progress in this area has been significant and reflects the interplay between footprinting methods that identify the sequence specificity of drug binding, structural approaches that define conformational features in the crystalline and solution states, hydrogen exchange techniques that monitor transient base pair opening and calorimetric methods that partition the enthalpic and entropic contributions to the binding isotherm.

AUosteric proteins control and coordinate chemical events in the living cell. When Monod conceived that idea he said that he had discovered the second secret of life. The first was the structure of DNA. The theory as published by Monod et al. (1963) was concerned chiefly with cooperativity and feedback inhibition of enzymes, such as the inhibition of threonine deaminase, the first enzyme in the pathway of the synthesis of isoleucine, by isoleucine, and its activation by valine. Two years later the theory was formalized by Monod et al. (1965).