The effect of EDTA and metal cations on the 5-bromoindoxyl acetate esterase activity in the thyroid of the guinea pig.

Miscellaneous metal cations and EDTA have been used as activators and inhibitors of esterase activity in the thyroid of the guinea-pig. The results indicate that the 5-bromoiondoxyl acetate esterase in the epithelial cells probably consists of two different A-esterase isoenzymes, one present in group I cells (the para-, intra-, and inter-follicular cells) and the other in group II cells (the follicular cells proper). The first isoenzyme seems to be calcium-dependent whereas the other is activated by various metal ions. Ca2+ + Mn2+ and Ca2+ + Co2+ were found to activate the esterase activity in group I cells. EDTA and Mn2+, on the other hand, activated the esterase activity in group II cells.