一、膜受体的分类

随着越来越多的膜表面受体被纯化，其结构及转导信号的方式逐步得以阐明。目前，按照受体的结构及其作用方式可将其分为三大类。这三大类受体在配体种类、受体的一般结构和功能及细胞对之发生反应的方式上有所不同，见表21－2。

Table 21－2　Classification of MembraneReceptors:Characteristics of Three Groups of Receptors

Characteristics	Ion Channel Receptors	G-Protein-Linked receptors	Recetpors with a Single Transmembrane Domain
Endogenous ligands	Neurotransmitter	Neurotransmitter	Growth factor hormone
		Hormone	Cytokine
		Auloacoid
		Chemotactic factor
		Exogenous stimulant
Structure	Oligomer with a pore	Probably monomer	Monomer of oligoner
			with (±）catalytic
			domain
Number of transmem	Four per subunit	Seven	One per subunit
bane segments
Function	Ion channel	Activation of G proteins	Tyrosine kinase
			Giuanylate cyclase(?)
Cellular responses	Depolarization or	Depolarization or	Regulation of function
	hyperpolarization	hyperpolarization	and expression of
		Regulation of function	proteins
		and expression of	Proliferation or
		proteins	differentiation