EFFECT OF HYPOTHYROIDISM ON THE SUBCELLULAR-DISTRIBUTION OF CA2-STIMULATED PROTEIN-KINASE-II IN CHICKEN BRAIN DURING POSTHATCH DEVELOPMENT(CALMODULIN)

In developing chicken brain Ca2+/calmodulin-stimulated protein kinase II (CaMPK-II) changes from being primarily cytosolic to being primaril y particulate during the protracted maturation period. To investigate whether thyroid hormone levels may be involved in regulating this subc ellular redistribution, we raised chickens from 1 day posthatching on food soaked in 0.15% (wt/vol) propylthiouracil (PTU) plus 0.05% (wt/vo l) methimazole (MMI). This produced a mild hypothyroidism specifically during the maturation period and resulted in a 67% reduction in the l evels of free triiodothyronine (T-3) at 42 days. The concentrations of alpha- and beta-CaMPK-II in cytosol (S3) and crude synaptic membrane (P2M) fractions from forebrain were measured by three methods: Ca2+/ca lmodulin- or Zn2+-stimulated autophosphorylation or binding of biotiny lated calmodulin. By all three methods hypothyroid animals showed a ma rked retardation of the redistribution of both subunits of CaMPK-II: a n increase in the concentration of the enzyme in S3 and a correspondin g decrease in P2M with no overall change in the total amount of enzyme and little apparent change in the concentration of other proteins, In both fractions, there was a parallel change in the Ca2+/calmodulin-st imulated phosphorylation of endogenous protein substrates but no chang e in the basal or cyclic AMP-stimulated protein phosphorylation. Suppl ementing the PTU/MMI-treated diet with thyroxine (0.5 ppm) prevented a ll of the observed changes.