SPECIFIC AIMS: 1. To learn more about the possible function of homocarnosine and carnosine in the central nervous system by studying the enzyme system which catalyzes the synthesis of these dipeptides. This would entail further purification of the enzyme system, so that its mechanism could be studied. The factor controlling the enzymatic reaction will be investigated, and the properties compared from different brain areas. 2. The study of the metabolism of intracerebrally injected (14C) carnosine and (14C) homocarnosine will be continued. The metabolites in brain and urine will be determined under normal and experimental conditions. These studies will be directed toward possible clinical application. In addition, the degradative enzyme may be studied in an attempt to find a specific inhibitor. 3. Another approach to the study of the possible function of these dipeptides will be a study of the distribution in discrete brain areas under a variety of experimental conditions. This will be accomplished by the development of a radioimmunoassay method.