The cell surface receptors that have intracellular domains associated with enzymes are called enzyme-linked receptors. The added molecule was water-soluble and cannot pass through the membrane to bind to intracellular receptors. Binding of the added molecule to the enzyme-linked receptor led to the activation of associated enzymes to generate the response (down-regulation of expression of the target gene).
Examples of enzyme-linked receptors include tyrosine kinase receptors. Binding of the signaling molecule to these receptors triggers phosphorylation of the intracellular domain which in turn transmits the signal to the cytoplasmic messenger.
