The objective of this grant application is to investigate the physiological and biochemical consequences of the genetic deficiency of a major cell- surface peptidase, namely dipeptidylpeptidase IV (DPP IV). Availability of an animal model in which there is an inheritable deficiency of DPP IV makes this project unique. Even though DPP IV deficiency in this animal model is a generalized phenomenon probably resulting in functional impairment of several organs, the present project will concentrate on the consequences of DPP IV deficiency in two major organs, small intestine and kidney. Since DPP IV plays an important role in the assimilation of dietary proteins in the small intestine and in the conservation of amino nitrogen in the kidney, this project will greatly advance our understanding of the involvement of DPP IV in the maintenance of protein nutrition of an animal. All studies will be done in parallel in Japan Charles River F344 rats (DPP IV-negative) and USA Charles River F344 rats (DPP IV-positive). Since the human small intestine and the human kidney possess high activity of DPP IV, this proposal is directly relevant and useful to the advancement of human health. The results of this project, in addition to enhancing our knowledge of the functional role of DPP IV in the small intestine and kidney, may also have potential use in the design and execution of future projects involving the DPP IV-negative animal model to investigate the function of DPP IV in biological processes of other organs. The studies are designed to characterize the transport of small peptides in intestinal and renal brush border membrane vesicles isolated from DPP IV-positive and DPP IV-negative rats, investigate any impairment in the processing of oligo- and polypeptides by intestinal and renal epithelial cells in DPP IV- negative rats and delineate the role of DPP IV in overall protein nutrition of the mammal. The DPP IV-negative rats also offer an ideal experimental tool to study the modulation of absorptive and secretory functions of the small intestine by the food-derived opioid peptides, namely beta- casomorphins. All experiments will be done using three different tissue preparations, purified brush border membrane vesicles, isolated cells and intact organs. In addition, experiments are proposed to delineate the molecular mechanism underlying the deficiency. This goal will be achieved by employing molecular biology approaches which include isolation of genomic DNA for DPP IV from DPP IV-positive and DPP IV-negative rats, comparison of restriction mapping of the DNAs and sequence analysis of the restriction fragments.