Lipase is widely found in animals, plants and microorganisms. Plants that contain more lipase are the seeds of oil crops, such as castor seeds and rapeseed. When oil seeds germinate, lipase can work in conjunction with other enzymes to catalyze the decomposition of oils and fats to produce sugars, providing the seeds with the ability to take root. Nutrients and energy necessary for germination; the pancreas and adipose tissue of higher animals contain more lipase in the animal body. There is a small amount of lipase in the intestinal juice, which is used to supplement the lack of fat digestion by pancreatic lipase. In carnivorous animals The gastric juice contains a small amount of butyrinase. In animals, various types of lipases control processes such as digestion, absorption, fat reconstruction, and lipoprotein metabolism; lipases are more abundant in bacteria, fungi, and yeasts (Pandey et al.). Since there are many types of microorganisms, they reproduce quickly and are prone to genetic variation, they have a wider pH range, temperature range and substrate specificity than animals and plants, and lipases derived from microorganisms are generally secreted extracellular enzymes. The main fermentation microorganisms are Aspergillus niger, Candida, etc. It is suitable for industrial large-scale production and obtaining high-purity samples. Therefore, microbial lipase is an important source of industrial lipase. Generally, the properties of lipase from different sources are different and it is also of great significance in theoretical research.
Lipase is a type of enzyme with a variety of catalytic abilities. It can catalyze the hydrolysis, alcoholysis, esterification, transesterification and reverse synthesis of triacylglycerides and other water-insoluble esters. In addition, It also exhibits other enzyme activities, such as phospholipase, lysophospholipase, cholesterol esterase, acylpeptide hydrolase activity, etc. (Hara; Schmid). The different activities of lipase depend on the characteristics of the reaction system, such as promoting ester hydrolysis at the oil-water interface, while enzymatic synthesis and transesterification can be achieved in the organic phase.
The catalytic characteristic of lipase is that its catalytic activity is greatest at the oil-water interface. Sarda and Desnnelv discovered this phenomenon as early as 1958. Water-soluble enzymes act on water-insoluble substrates, and the reaction occurs at the interface of two completely different phases that are separated from each other. This is a characteristic that distinguishes lipase from esterase. The substrate of esterase (E C3.1.1.1) is water-soluble, and its optimal substrate is esters formed from short-chain fatty acids ( Less than or equal to C8).
Lipase is one of the important industrial enzyme preparations. It can catalyze lipolysis, transesterification, ester synthesis and other reactions, and is widely used in oil processing, food, medicine, daily chemical and other industries. Lipases from different sources have different catalytic characteristics and catalytic activities. Among them, the large-scale production of lipases with transesterification or esterification functions for organic phase synthesis is of great significance for the enzymatic synthesis of fine chemicals and chiral compounds.
Lipase is widely distributed among microorganisms, and its producing bacteria are mainly molds and bacteria. There are 33 published lipases from different sources suitable for triglyceride processing, 18 of which are from molds and 7 from bacteria.
Lipase has an affinity for the oil-water interface and can catalyze the hydrolysis of water-insoluble lipid substances at a high rate at the oil-water interface; lipase acts on the hydrophilic-hydrophobic interface layer of the system, which is also different from esterase a characteristic.
Lipases from different sources may have large differences in amino acid sequences, but their tertiary structures are very similar. The active site residues of lipase are composed of serine, aspartic acid, and histidine, and they belong to the serine protease class. The catalytic site of lipase is buried in the molecule, and its surface is covered by a spiral cap-like structure formed by relatively hydrophobic amino acid residues (also known as the "lid"), which protects the triplet catalytic site. The amphipathic nature of the -helix in the "lid" will affect the binding ability of lipase to the substrate at the oil-water interface, and its weakened amphipathicity will lead to a reduction in lipase activity. The outer surface of the "lid" is relatively hydrophilic, while the inner, facing surface is relatively hydrophobic. Due to the association between lipase and the oil-water interface, the "lid" opens and the active site is exposed, which enhances the binding ability of the substrate to lipase. The substrate can easily enter the hydrophobic channel and combine with the active site to form Enzyme-substrate complex. The interfacial activation phenomenon can increase the hydrophobicity near the catalytic site, causing the -helix to reorient, thus exposing the catalytic site; the presence of the interface can also allow the enzyme to form an incomplete hydration layer, which is beneficial to the aliphatic formation of hydrophobic substrates. The side chains fold onto the surface of the enzyme molecule, making enzyme catalysis easier to proceed.
