Abstract
The distinctive function of nitric oxide (NO) in biology is to transmit cellular signals through membranes and regulate cellular functions in adjacent cells. NO conveys signals as a second messenger from a cell where NO is generated to contiguous cells in two ways; one is as gaseous molecule by free diffusion resulting in an activation of soluble guanylate cyclase (NO/cGMP pathway), and another form is by binding with a molecule such as cysteine or protein thiol through S-nitrosylation (SNO pathway). Both pathways transmit much of the biological influence of NO from cell where other messenger molecules but NO are confined, through the plasma membrane to the adjacent cells. Since SNO pathway cannot utilize free-diffusion mechanism to get through the membrane as the molecular size is significantly larger than NO molecule, it utilizes amino acid transporter to convey signals as a form of S-nitrosylated cysteine (CysNO). Although S-nitrosylated glutathione (GSNO) is the molecule which act as a determinant of the total S-nitrosothiol level in cell, transnitrosylation reaction from GSNO to CysNO is an initial requirement to pass through signal through the membrane. Thus, multiplexed combination of these steps and the regulatory factors involved in this system conform and modify the outcome from stimulus-response coupling via the SNO pathway.