The chemical nature of the modifications in the primary structure of enzyme molecules from old animals will be pursed by cyanogen bromide and tryptic digest followed by "finger printing" and also gel electrophoresis. The enzymes used in this study will be rat superoxide dismutase (SOD) and rabbit liver and muscle aldolases. The physiological consequences of the accumulation of inactive enzyme molecules in aging animals will be studied. Here the effects of elevated O2 concentrations on SOD and catalase levels in lung, liver, erythrocytes, heart and brain of mice and rats of various ages. Also, catalase activity will be related to the resistance of mice of varying ages to administered H2O2. Studies on the properties of choline acetyl transferase in various parts of the brain and spinal cord of aging animals will be studied. This will be related to the known decline in neurotransmission with age recorded by others. Regeneration of liver in animals of different ages will be studied. The specific aim is to study polyamine synthesis and the properties of ornithine decarboxylase in relation to the rate of growth of the regenerating system. The degradation of total and specific proteins, by the double label technique of Schimke and the use of monospecific antibodies, will be studied in liver, heart, brain and skeletal muscle of mice of varying ages. The studies will attempt to investigate whether alterations of the degradation system or proteins of old cells are responsible for the slower degradation encountered in old cells.