Our lab studies mutant strains of the free-living nematode, Caenorhabditis elegans, with the goal of learning more about neurotransmitter biosynthesis and the genes that regulate it. One particular mutant, cat-4, is deficient in the neurotransmitters serotonin and dopamine and is hypersensitive to various chemical agents. The cat-4 gene likely encodes an enzyme that makes a cofactor needed for serotonin, dopamine, and tyrosine synthesis. Cuticle proteins in closely related species are covalently cross linked at tyrosine residues, forming di- and trityrosine. We hypothesized that the cuticle defect in cat-4 mutants might be caused by reduced tyrosine. Our approach to detect cross linking involves two methods: 1) Analysis of the hydroyslate of isolated cuticles by High Performance Liquid Chromatography (HPLC) and 2) Immunocytochemical detection using a monoclonal anti-dityrosine antibody. We have so far adapted an antibody staining technique that can be used on C. elegans and synthesized and purified di- and trityrosine standards. We hope to quantify the differences between mutant and wild type cuticles using a derivative (AMQ) to increase the sensitivity of HPLC detection.