Polyamines in clinical and basic science: introductory remarks.

The most commonly occurring of the natural polyamines are putrescine [ Nl ll(CI ll),N14?, a diaminel, spermidine [ Nl 12(C€12)3Nl l(C142),NIIl. a triamine] and spermine [ Nl il(Cl 12);NI l(C€Il),N€I(CI 1?)?NI ?. a tetramine]. One or more of these compounds are present in every living cell. All are found in eukaryotes; spermine is absent from most prokaryotes. The polyamines are essential for cell growth and differentiation [ 1-3 ]. Their concentrations vary with the cell cycle, and induction of polyamine biosynthesis is one of the first events in cell proliferation, preceeding both protein and nucleic acid synthesis. lntracellular polyamine concentrations are subject to elaborate control by both biosynthetic and catabolic reactions. In addition, most cells appear to possess a polyamine transport system that can, under appropriate conditions, substitute for synthesis de nooo 14.51. and may also be the mechanism by which cells in culture secrete excess polyamines into the medium [ h I. What do the polyamines do? At present there is no satisfactory answer to this question. The polyamines influence a confusingly large number of biological processes but the molecular mechanisms by which they do this are still largely unknown. In mammals, the enzymes of polyamine metabolism have been well conserved in evolutionary terms, as shown by the high degree of similarity demonstrated by sequence data for the ornithine decarboxylases [7], S-adenosylmethionine decarboxylases [ 81 or spermine/spermidine N’-acetyltransferases [ 9 1 isolated from different sources. This, in turn, points to the underlying importance of the polyamines in living cells.