Influence of polyamines on membrane functions.

Polyamines (putrescine, spermidine and spermine) are ubiquitous polycationic metabolites in prokaryotic and eukaryotic cells. Their roles in the regulation of major functions in cell growth, cell differentiation and their intricate and exquisitely regulated biosynthetic pathways have attracted considerable attention during the last few decades. Authoritative reviews and books have dealt with these aspects, including the design of enzyme inhibitors which by depleting cells of their normal polyamine contents provoke cell growth arrest and other pharmacologically important phenomena (see, e.g., Heby, 1981; Pegg & McCann, 1982; Tabor & Tabor, 1984; Pegg, 1986, 1988; McCann, e al., 1987). Although the functions attributed to the polyamines are numerous, their modes of action at a molecular level remain a matter of speculation. Because of their protonated amino groups (at physiological pH values), polyamines are known to bind to negatively charged cellular macromolecules such as nucleic acids. This has been amply documented and studied, and it is thought to explain many of the polyamine-related effects at the cellular level (Marton & Morris, 1987). In agreement with that notion, interactions of polyamines with components of membranes, such as acidic (phospho)lipids or negatively charged residues of membrane-bound proteins, are to be expected which could affect some properties of biological membranes. Because of their cationic nature, polyamines present many characteristics of inorganic cations such