10.9 Lipases and esterases

Lipases and esterases catalyse the hydrolysis of esters made between alcohols and organic (‘fatty’) acids. They generally have low specificity and any lipase will hydrolyse virtually any organic ester, though different esters will be acted upon at different rates, and strictly speaking all these enzymes are carboxylester hydrolases. The main factors influencing what specificity is expressed are the lengths and shape of hydrocarbon chains either side of the ester link. The term esterase is generally applied to enzymes ‘preferring’ short carbon chains in the acyl group. Lipases are lipolytic enzymes which are a special class of carboxylester hydrolases capable of releasing long-chain fatty acids from natural water-insoluble carboxylic esters. Their substrates include fats, the lipid components of lipoprotein and the ester bonds in phospholipids. Rather than attempting to differentiate ‘lipases’ from ‘esterases’ using other criteria, it is probably best to remember that lipids, by definition, are insoluble in water and to distinguish lipolytic esterases (acting on lipids) from nonlipolytic esterases (not acting on lipids) (Ali et al., 2012).

Extracellular lipase production has been detected in Agaricus bisporus during degradation of bacteria. In fermenter cultures most of the lipase is produced in the stationary phase (i.e. is a secondary metabolic activity) and regulation of lipase production in Rhizopus is very much affected by carbon and nitrogen sources in the medium and by the oxygen concentration.

Lipases are generally strongly activated by water-lipid interfaces (the active site of these enzymes is a hydrophobic cavity). These enzymes are able not only to catalyse the hydrolysis of triglycerides to free fatty acids, diglycerides and monoglycerides under aqueous conditions, but they are also able to carry out synthetic, and trans- and inter-esterification reactions in the presence of organic solvents. Add to these features stability and broad substrate specificity and you can begin to understand the biotechnological interest in these enzymes as commercial chemical catalysts (Barriuso et al., 2013).

Updated July, 2018