DEVELOPMENTAL REGULATION OF PROTEIN PHOSPHATASE TYPE-1 AND TYPE-2A INPOSTHATCH CHICKEN BRAIN

The activity and subcellular distribution of protein phosphatases I an d 2A were measured in chicken forebrain and cerebellum during post-hat ch development. At all post-hatch ages, a large proportion of PPI and PP2A was membrane bound and these enzymes were less active than their cytosolic counterparts. The protein concentration of PPI in the membra nes increased 40% between 2 and 14 days and a further 60% between 14 d ays and adult, whereas the PPI enzyme activity in the membranes progre ssively decreased. In contrast to PP1, the protein concentration of PP 2A remained constant in all fractions during post-hatch development, a nd the enzyme activity of PP2A did not change except for a decrease in the membrane-bound activity between 2 and 14 days. These results show that the subcellular distribution and activity of PP1 is selectively regulated during post-hatch development and that membrane association and inactivation of PP1 are independent events.