The long-range goal of this research is to regulate the loss of nitrogen, wasting complications and tissue destruction associated with the juvenile-onset insulin-dependent form of diabetes mellitus and other diseases. Our approach is to identify and characterize cellular proteinases and mechanisms used by living systems to degrade cellular proteins and regulate the rate of degradation of proteins in general and specific enzymes according to the metabolic needs of the organism. Aspects of this goal include determination of the initial or rate-limiting steps in the process of enzyme degradation, the influence of hormones on protein turnover and the identification of cellular proteinases active in normal and diseased states. Our working hypothesis based on previous studies is that the mechanisms regulating the degradative process involve factors that alter the conformation of cellular proteins. In this proposed project, liver arginase and muscle aldolase will be used as model cytosolic proteins to determine how the diabetic state and ligands that interact with proteins alter the turnover of enzymes. The synthesis and degradation of arginase and aldolase and the physical-chemical properties of these enzymes from normal and diabetic animals will be studied. We will investigate the interaction of aldolase and arginase with ligands that may regulate protein conformation (branched chain amino acids, disulfides, nucleotides) and determine how the concentrations of these ligands change in tissues with altered rates of degradation. In addition, we recently discovered the first heritable deficiency of a mammalian cellular proteinase; a kidney brush-border metallo-endoproteinase, meprin, is lacking in certain inbred strains of mice. This discovery creates the opportunity to determine the molecular basis of a unique cellular proteinase deficiency. In addition, we plan to investigate the possible role of the proteinase in peptide hormone degradation, in kidney protein degradation and in diabetic nephropathy. Renal complications in diabetes mellitus in man are among the most serious; our studies with diabetic mice will aim to determine whether the kidney proteinases play a role in the pathogenesis of renal disease. These studies have both biological and medical significance and will add to our knowledge of the role of proteinases and mechanisms of protein turnover in mammalian cells.
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