The overall objective of this investigation is to gain a better understanding of the induction, regulation and physiologic role of peroxidase activity in the normal and neoplastic mammary gland; further, to evaluate the increased peroxidase activity and iodine uptake of mammary tumors for their diagnostic potential and correlation with hormone response of the tumors. To this end the enzymatic peroxidase activity and protein iodination will be studied: 1) in the rat mammary gland under various hormone influences, during iodine deficiency, and during mammary carcinogenesis and 2) in rat mammary tumors. Peroxidase activity will be assayed in salt extracts of the tissues using the guaiacol oxidation assay and the activity compared with in vivo and in vitro tissue uptake of radiolabelled iodine and iodine incorporation into protein. Qualitative changes in iodinated proteins will be assessed by two-dimensional gel electrophoresis. The effects of hormones, especially estrogen, progesterone and prolactin, on the induction and regulation of peroxidase activity in normal and neoplastic mammary tissue will be elucidated. The results of various endocrine manipulations on mammary tumor growth will be correlated with tumor peroxidase activity. Peroxidase enzymes will be purified and characterized from mammary gland and tumors and variations in peroxidase isoenzyme patterns in these tissues will be studied. Kinetics of peroxidase synthesis, assembly from apoenzyme and porphyrin, and degradation will be investigated.