Mammary Gland Enzyme Systems Concerned with Synthesis of Monoiodotyrosine.

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Abstract
Lactating mammary tissue was incubated with I131-iodide at 38°C in TC 199 Medium or Ringer-Phosphate buffer at pH 7.4 and digested overnight with pancreatin at pH 8.0. Iodinated compounds were separated by paper chromatography, radioautographed, and the radioactive spots counted separately. In fresh tissue 44 to 52% of I131 taken up was found in monoiodotyrosine. Mammary tissue stored at 7°C for 6 days prior to iodination showed a 3-fold increase in I131 accumulation, but proportion of MIT formed was similar to that in fresh tissue. Both I131 uptake and percentage MIT formation decreased progressively during mammary involution, indicating that mammary iodine metabolism is related to lactation. MIT formation was blocked by boiling, by thiouracil (0.04 mg/ml) and reduced by KSCN (0.1 mg/ml). Tissue homogenates were separated into soluble and mitochondrial-microsomal fractions by centrifugation. Soluble fraction from parotid and lactating mammary glands, but not from liver, formed MIT from added tyrosine. MIT formation was catalyzed by Cu++ and increased further by Cu++ + Mn++. Mitochondrial fraction from lactating mammary tissue formed MIT without addition of tyrosine substrate or metal catalyst. All except traces of MIT in this system was in combined form until released by hydrolysis with pancreatin.