The role of certain microbial metabolites as specific complexing agents.

The discovery of microbial metabolites—macrotetrolides, siderochromes and boromycin—is reviewed. The structures of these and related compounds provide instructuve examples of how Nature has solved the problem of cornplexing certain rarer elements, such as potassium, iron and boron. The common structural features of these highly specific, natural complexing agents are briefly discussed. It was emphasized by Academician M. M. Shemyakin in his opening lecture' and it was confirmed explicitly or implicitly by all following plenary lecturers that the chemistry of natural compounds has changed considerably in the 'sixties from descriptive natural history of individual compounds towards a bioorganic chemistry that overlaps with biochemistry and molecular biology. We believe today that in the structure of natural compounds we find wisdom collected by living matter during several hundred millions of years. Natural compounds are the result of hundreds of millions of years of chemical experimentation of living organisms controlled by evolution and perhaps other hitherto undiscovered factors. In spite of the great progress in understanding biological phenomena on a molecular basis, we still do not know most of the essential structural details of natural biological tools. We can therefore still learn a great deal by investigating natural compounds. By doing so we shall not perhaps reach the level of the supreme wisdom, but the results can serve as a useful starting point in the terrifying multidimensional space of research possibilities in biological sciences. One fascinating research subject in this respect is the study of the specific cornplexing agents by which organisms concentrate within their bodies elements that are essential for life but occur in Nature either accompanied by a large excess of similar elements (e.g. potassium), or are widely spread but in low concentrations (e g. boron, cobalt, copper, iron, molybdenum, zinc etc). In what form do organisms bring these elements in the right concentrations at the right time to the right place, i.e. to the interior of the cell or its subunits, where they are needed? I would like to illustrate this question by a few examples found by investigating microbial metabolites by a research