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Schematic representing the phosphorylation of tyrosine hydroxylase (TOHase) by four protein kinase systems in adrenergic chromaffin cells. Acetylcholine is responsible for the Ca+-mediated changes whle VIP or PACAP appear responsible for the Kinase A- , and possible the Kinase C-, mediated phosphorylation. Also shown is the possibility that Ca++may also stimulate cAMP production through stimulation of Ca++ sensative adenylyl cyclase. It is not yet known which of these mechanisms is predominately responsible for catecholamine synthesis regulation
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