Previous symposia on Metabolic Interconversion of Enzymes were held in 1970 (Santa Margherita-Ligure, Italy), 1971 (Rottach-Egern, Ger- many), 1973 (Seattle, USA) and 1975 (Arad, Israel). The present pub- lication reports the proceedings of the 5th International Symposium on Metabolic Interconversion of Enzymes, held in Titisee/Black Forest (Germany) from October 1st-5th, 1980. In the last few years, the number of enzymes for which control of activity by enzyme-catalyzed covalent modification, i.e., by intercon- version, is of recognized metabolic importance has increased so much that is was not possible to have every such enzyme considered during a 3-day conference. The organizers therefore decided to devote only one of the three sections to "metabolic interconversion" per se, and to cover in the other two sections "enzyme regulation by proteolytic modification" and "novel aspects of regulation". According to the IUP AC-IUB Commission on Biochemical Nomenclature (cf. J. Biol. Chem. 252,5939-5941 (1977)), modification by proteolysis is not in- cluded in "metabolic interconversion". Considering, however, the close interrelationship of these two types of enzyme control, it has become a tradition, beginning with the conference in Rottach-Egern 1971, to include proteolytic modification in our conferences.

Proteinases were among the first enzymes to be investigated biochemi- cally, and purification and crystallization especially of proteolytic enzymes of the digestive tract has contributed much to our present knowledge of enzymic structure and mechanisms of catalysis. However, for a long time little has been known about the functional aspects of proteinases. The only exception from this have been the digestive tract enzymes responsible for extracellular catalysis of protein breakdown and supply of amino acids for new-protein assembly and nitrogen metab- olism in the respective organs. The work of Schoenheimer, summarized for the first time in 1942 in a paper entitled "Dynamic state of body constituents", showed that continuous turnover of proteins takes place in cells. But scientists did not pay much attention to these findings at that time. The continuous accumulation of knowledge of a variety of intracellular proteolytic processes during the past decades has greatly stimulated research in this field. The central role of proteo- lysis in cellular regulation has become fully evident during recent years. It is the aim of the 30th Mosbach Colloquium to present an over- view of our present knowledge of proteinase structure, function and control. The relationship between globular protein structure of a proteinase and induction of enzymic activity will be discussed for trypsin and trypsinogen activation. One significant proteinase action is the total degradation of proteins to serve cellular needs under different condi- tions.