Volume V deals with the problems of turnover in the nervous system. "Turnover" is defined in different ways, and the term is used in different contexts. It is used rather broadly in the present volume, and intentionally so. The turnover of macromolecules is only one aspect; here "turnover" in dicates the simultaneous and coordinated formation and breakdown of macromolecular species. The complexities of cerebral protein turnover are shown in a separate chapter dealing with the synthesis of proteins, in another on breakdown, and in still another on the relationship of these two (showing how the two halves of turnover are controlled). The fact that most likely the two halves of protein turnover, synthesis and breakdown, are separated spatially and the mechanisms involved are different further emphasizes the complexity of macromolecular turnover. "Turnover" is used in a different context when the turnover of a cycle is discussed; but here again a number of complex metabolic reactions have to be interrelated and controlled; some such cycles are discussed briefly in this volume, additional cycles have been discussed with metabolism, and some cycles still await elucidation or discovery.

The purpose of the present volume, the first of two on the pharmacology, biochemistry, and physiology of cyclic nucleotides, is to provide a comprehensive and up-to-date anthology on the nature and role of these important chemical regulators. Each of the chapters is the work of internationally known researchers who present a lucid and detailed review of their subject and not merely a single laboratory's viewpoint. The chapters emphasize critical assessments of the field rather than mere listings of experimental findings. By so doing, the contributors present the role of cyclic nucleotides in relationship to other intracellular regulators. Each chapter begins with a detailed summary to allow the reader to obtain a rapid overview of subsequent material. In addition, there are extensive bibliographies and a detailed subject index. Wherever pertinent, the chapters contain sections on drug mechanisms, physiological relevance, and disease processes. The Volume is divided into two sections, each beginning with an overview written by Professors T. W. RALL and P. GREENGARD, respectively. The first section focuses on the detailed pharmacology and chemistry of cyclic nucleotides, including their formation, degradation, measurement, and interaction with various modulatory agents, such as receptors and calcium. The second section is concerned with the biochemistry of protein phosphorylation, a process which appears to be one of the most important mechanisms for the intracellular expression of cyclic nucleotide action in eukaryotic cells.