Protein-tyrosine phosphatases (PTPases) that regulate steady-state insulin signalling by dephosphorylating the active form of the insulin receptor (IR) kinase as well as post-IR substrates in insulin-sensitive cells have been implicated in the pathogenesis of insulin-resistance in disease states, including common conditions such as obesity and non- insulin-dependent diabetes (NIDDM), where the insulin resistance also appears to contribute to increased cardiovascular morbidity and mortality. This project will test the hypothesis that changes in overall tissue PTPase activity and the abundance of specific candidate PTPase enzymes that may regulate the insulin signalling pathway are involved in the insulin resistance in adipose tissue and skeletal muscle in human subjects with obesity and NIDDM. The following major Specific Aims are proposed: Aim 1. Measure PTPase activity against the IR and phosphorylated lysozyme and the abundance of several candidate PTPases in subcutaneous adipose tissue and skeletal muscle from lean and obese (body mass index greater than 30 kg/m2) subjects, both with and without Type II diabetes; Evaluate these cross-sectional data on PTPases for possible associations with tissue-specific insulin sensitivity, body fat content, insulinemia, and hyperglycemia. Aim 2. Use clamp techniques in lean and obese subjects to evaluate the effect of hyperglycemia and hyperinsulinemia on PTPase activity and enzyme in skeletal muscle and adipose tissue; Study whether significant weight loss in a group of non- diabetic obese individuals or achieving glycemic control in a group of recently diagnosed subjects with NIDDM is associated with alterations in adipose tissue and muscle PTPase activity and abundance. Aim 3. Treat isolated human adipose cells with high glucose and/or insulin in vitro to determine whether PTPase activity or abundance is affected by incubation with these components of the diabetic milieu. These studies will determine in two of the major tissues involved in glucose metabolism whether PTPase activity or the abundance of specific PTPases is associated with human insulin resistance and provide further support for potential new therapeutics that could ameliorate insulin resistance by inhibiting PTPases in insulin target tissues.