Membrane Fluidity Research Paper

2.7.3 Membrane fluidity

Membrane fluidity, or known as the reciprocal of viscosity, was used to describe the extent of disorder and the molecular motion within the lipid bilayer (Cossins, 1994; Murata & Los, 1997). Unsaturated membrane lipids are the major factor that affect the fluidity of membrane lipids (Murata & Los, 1997). A decrease in temperature leads to a decrease in membrane fluidity, which will further trigger the expression of the genes for fatty acid desaturases. These enzymes play a role to introduce double bonds into the fatty acyl chains of membrane lipids to counterbalance the decrease in membrane fluidity. As a result, the physical properties of the membrane can be restored to their optimal state, which will have a balanced maintenance of the ion gradients across the membranes, and the restoration of the functions of membrane associated enzymes.

There are three types of fatty acid desaturases that have been described, such as acyl-CoA desaturases, Acyl-ACP desaturases and acyl-lipid desaturase. All of these fatty acid desaturases introduced a double bond into the fatty acids bound to the CoA, ACP and glycolipids sites (Chintalapati et al., 2004; Russell, 1997). Among all of the desaturases, acyl-lipid desaturases was known to be the most efficient fatty acids

cereviase. Phosphorylation of His kinase will respond with an increase in ambient osmolarity and transduces the signal to mitogen-activated protein kinases cascade Murata & Los, 1997). Besides His Kinase, another potential sensor is a Ca2+ channel. However, Ca2+ channel was only found in higher plant and such channel has not been fully characterized. Ca2+ channel opens at low temperatures during the decrease of membrane fluidity, and the entering Ca2+ ions will activate a signal transduction pathway for the up-regulation of the expression of low temperature inducible genes (Monroy & Dhindsa,