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首页> 外文期刊>Journal of Neurochemistry: Offical Journal of the International Society for Neurochemistry >Membrane-bound histamine N-methyltransferase in mouse brain: possible role in the synaptic inactivation of neuronal histamine.
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Membrane-bound histamine N-methyltransferase in mouse brain: possible role in the synaptic inactivation of neuronal histamine.

机译：小鼠脑中的膜结合组胺N-甲基转移酶：在神经元组胺的突触失活中可能发挥作用。

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摘要

In the CNS, histamine is a neurotransmitter that is inactivated by histamine N-methyltransferase (HNMT), a soluble enzyme localized to the cytosol of neurons and endothelial cells. However, it has not been established how extracellular histamine, a charged molecule at physiological pH, reaches intracellular HNMT. Present studies investigated two potential routes of histamine inactivation in mouse brain nerve terminal fractions (synaptosomes): (i) histamine uptake and (ii) histamine metabolism by HNMT. Intact synaptosomes demonstrated a weak temperature-dependent histamine uptake (0.098 pmol/min-mg protein), but contained a much greater capacity to metabolize histamine by HNMT (1.4 pmol/min-mg protein). Determination of the distribution of HNMT within synaptosomes revealed that synaptosomal membranes (devoid of soluble HNMT) contribute HNMT activity equivalent to intact synaptosomes (14.3 +/- 2.2 and 18.2 +/- 4.3 pmol/min-tube, respectively) and suggested that histamine-methylating activity is associated with the membrane fraction. Additional experimental findings that support this hypothesis include: (i) the histamine metabolite tele-methylhistamine (tMH) was found exclusively in the supernatant fraction following an HNMT assay with intact synaptosomes; (ii) the membrane-bound HNMT activity was shown to increase 6.5-fold upon the solubilization of the membranes with 0.1% Triton X-100; and (iii) HNMT activity from the S2 fraction, ruptured synaptosomes, and synaptosomal membranes displayed different stability profiles when stored over 23 days at - 20 degrees C. Taken together, these studies demonstrate functional evidence for the existence of membrane-bound HNMT. Although molecular studies have not yet identified the nature of this activity, the present work suggests that levels of biologically active histamine may be controlled by an extracellular process.
机译：在CNS中，组胺是一种神经递质，可被组胺N-甲基转移酶（HNMT）灭活，组胺N-甲基转移酶是一种位于神经元和内皮细胞胞浆中的可溶性酶。但是，尚未确定细胞外组胺（一种在生理pH下带电的分子）如何到达细胞内HNMT。目前的研究调查了小鼠脑神经末梢部分（突触小体）中组胺失活的两种潜在途径：（i）组胺摄取和（ii）HNMT引起的组胺代谢。完整的突触小体显示出弱的温度依赖性组胺摄取（0.098 pmol / min-mg蛋白质），但具有更高的HNMT代谢组胺的能力（1.4 pmol / min-mg蛋白质）。确定HNMT在突触体内的分布表明，突触体膜（无可溶性HNMT）贡献的HNMT活性相当于完整的突触体（分别为14.3 +/- 2.2和18.2 +/- 4.3 pmol / min-管），并建议组胺-甲基化活性与膜级分有关。支持该假说的其他实验发现包括：（i）在使用完整的突触小体进行HNMT分析后，仅在上清液级分中发现了组胺代谢物远程甲基组胺（tMH）; （ii）当用0.1％Triton X-100溶解膜时，膜结合的HNMT活性显示增加6.5倍; （iii）S2级分，突触小体和突触膜的HNMT活性在-20摄氏度下保存23天时显示出不同的稳定性。这些研究合在一起证明了膜结合型HNMT的功能性证据。尽管分子研究尚未确定这种活性的性质，但目前的工作表明，生物活性组胺的水平可能受细胞外过程的控制。

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