Calcium Effects on the Solubilization of Membrane‐Bound Histidine Decarboxylase in the Rat Brain

Abstract

In a previous work we have shown that histidine decarboxylase (HD) activity is found in a soluble and a membrane-bound form. A major part (82%) of the membrane-bound HD activity in the crude mitochondrial fraction (P2) was present in the synaptic plasma membrane-containing subfraction. Physiological concentrations of Ca2+ had no direct effect on HD activity but caused a solubilization of approximately 50% of membrane-bound HD in the P2 fraction. Mg2+ had similar but lower effects (20% solubilization) than Ca2+. Incubation with depolarizing concentrations of K+ in the presence of 1 mM CaCl2 caused a significant (30%) solubilization of HD.

Intracellular Localization of the 74- and 53-kDa Forms ofl-Histidine Decarboxylase in a Rat Basophilic/Mast Cell Line, RBL-2H3

“…However, the intracellular localization of HDC remains to be clarified. In addition to the soluble form of HDC, membrane-associated HDC activity has been reported in various tissues, such as rat hypothalamus (24) and rat brain (25)(26)(27)(28). However, these reports did not refer to the molecular size of the membranous HDC.…”