Binding of thyroid hormone to isolated ovarian nuclei from a freshwater perch, anabas testudineus

Abstract

>High affinity, low capacity 3,5,3'-triiodo-L-thyronine (T₃) specific binding was detected in the pure nuclei preparation from ovarian tissue of freshwater perch by employing an in vitro thyroid hormone binding assay. Under standardized assay conditions of pH 7.0 at 30ο and 1 hr incubation time, the binding in the ovarian nuclei was saturable with a K_d 9.1 × 10^-9 M. For comparison, a Scatchard analysis of T₃ binding to perch hepatic nuclei was done and a higher K_d value (16.89 × 10^-9 M) with twofold increase in maximum binding capacity (MBC 8.882 and 4.312 pmol/mg DNA in liver and ovary, respectively) was observed. Competitive inhibition studies showed ovarian T₃ binding to be hormone specific with relative binding affinities comparable to T₃ binding in other systems. T₃ binding to the nuclear preparation from tail kidney and brain tissue of perch was considerably lower in comparison to liver and ovarian nuclei. Functional relevance of T₃ binding to perch ovarian nuclei was tested by incubating ovarian tissue in vitro with T₃. T₃ significantly (P < 0.001) increased protein synthesis in comparison to control.