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.
