Result of enzymatic activity of the receptor usually leads to recruitment of additional molecular changes thus causing a signal transduction "cascade". These intermediates often forms a second messenger system. Within the signal transduction cascade there may be enzymes and transporters which work similar way as receptors. Enzymatic activities include covalent modifications like proteolytic cleavage, phosphorylation/dephosphorylation, methylation/demethylation, ubiquitinylation/deubiquitinylation etc. These changes help regulate the propagation of the signal through the cell. An important phenomena that happens in the intracellular portion of signaling is signal amplification. During signal amplification, a few number of receptors are initially activated. The intracellular response results in multiple secondary messengers to be activated, thereby amplifying the initial signal.