Overview Nitrogen balance positive amino acid (AA) intake > excretion examples growth pregnancy negative AA excretion > intake examples kwashiorkor starvation infection AA absorption in intestine proteins degraded by trypsin and pepsin enteropeptidase cleaves trypsinogen (inactive) to trypsin (active) absorbed as AA's across the gut lumen with specific transporter for similar AA's e.g., transporter for basic AA's, transporter for large neutral AA's deficiencies lack of absorption with pancreatitis due to ↓ in degradative enzyme production Hartnup disease defect in large neutral AA transporter in the intestine and renal proximal tubule cells result is a tryptophan deficiency presents similar to pellagra AA absorption in kidney AA's that are filtered from the glomerulus can be actively reabsorbed in the proximal convoluted tubules with similar transporters as the gut deficiencies cystinuria genetic defect in transporter for cysteine, ornithine, lysine, arginine AR presentation cystine staghorn calculi note: cystine = 2x cysteine attached by a disulfide bridge cystine kidney stones result from high concentrations in urine treatment alkalinization of the urine with acetazolamide