Effects of EGTA and calmodulin, neutral thiol proteinases and protein kinase C inhibitors on loss of chicken pineal serotonin N-acetyltransferase activity.

This paper shows that the loss of chicken pineal serotonin N-acetyltransferase activity in crude homogenates of the pineal gland during preincubation at 37 degrees C is a complex process which seems to involve protein kinase C, calmodulin and calcium-activated neutral protease. All three compounds are strongly related to free calcium levels, and hence EGTA effectively prevents this loss of activity. It is proposed that the loss of serotonin N-acetyltransferase activity in crude chicken pineal homogenates is due to a series of molecular events, probably triggered by loss of the calcium gradient present in the intact gland by the homogenization process, leading to rapid serotonin N-acetyltransferase deactivation. In these homogenates two calmodulin inhibitors, a protein kinase C inhibitor and a neutral thiol proteinase inhibitor, and EGTA were found to markedly reduce the rate of serotonin N-acetyltransferase deactivation.