Functional diversities of Phospholipases within and outside living cells
International Journal of Agricultural and Food Science
The intracellular and exocellular phospholipases are components of living cells. The four major phospholipase classes PLA, PLB, PLC and PLD hydrolyse phospholipid bonds at specific locations of glycerol carbon. Many of them possess lysophospholipase activity and some are involved in synthesis of eicosanoids. The PLA consists of two regioselective sub-classes, namely, PLA 1 and PLA 2 ; and the later is further divided into sixteen different groups in terms of their structural and functional
... and functional identities. Protein-protein interaction, lipid-protein interaction, membrane permeability, cellular defence and digestion of nutrients are controlled by phospholipases. They have specific roles in hydrolysing plasmalogen and other plasma platelet-activating factors. The mechanism of hydrolysis of phospholipases is based on a heterogeneous catalytic system of two immiscible phases where calcium-ion enhances the rate of many phospholipase reactions. Either substrate level or enzyme level conformational changes are believed to be responsible for activation of these enzymes. The growing affinity of the enzyme for its substrate by overcoming enormous mass-transfer resistances by the products of reaction as well as by the physical state of substrate molecules and ions is attributed to these conformational changes. The classical proton-relay mechanism involving a single water molecule is confronted by the calcium-coordinated oxyanion mechanism. Under the calcium-coordinated oxyanion scheme, one molecule of water (W6) propagates the charge of catalytic site of histidine residue as nucleophile towards the substrate, while another (W5) coordinates to the cataionic calcium thereby facilitating the anionic substrate to come nearer to the enzyme for hydrolysis. Once their mode of action is well-understood, phospholipases outside the biological cells can be equally useful in food processing and chemical industries for purification and synthesis of several valuable products.