Lactase

• OMIM: 603 202
• UniProt: P09848

• CAS Number: 9031-11-2

Lactase ( technical terminology, standard language: lactase, LPH abbreviation, gene name: LCT ) is called the enzyme, the lactose ( milk sugar) into its component galactose ( mucus sugar) and glucose ( dextrose) splits. Without this chemical reaction, the components of the lactose can not be absorbed by the small intestine. In humans, the enzyme is normally produced in childhood in the small intestine, in Europe in most people later in adulthood. A lack of lactase can have several causes (see lactose intolerance ) and performs at 2/ 3 of the persons concerned to digestive problems if lactose is added.

The food industry uses enzymes that can hydrolyze lactose and also the preamble are assigned to β -galactosidases. In scientific parlance lactase should only be used for beta- galactosidases from mammals. Since the production of human lactase would be uneconomical, microbial beta- galactosidases mushrooms produced using biotechnology for food technology exclusively from safe and legal bacteria (Escherichia coli K -12), yeasts ( Kluyveromyces lactis ) or filamentous. The hydrolysis of lactose leads to a reduction of the lactose, wherein glucose and galactose which contribute in lactose-free milk in an increased sweetness. Lactose -free foods are not only sold to lactoseintolerante people, lactose- free ice cream for example, has more favorable processing characteristics and by other crystallization properties a finer texture.

In addition to lactase, the enzyme has another Glykosylceramidase activity, which is why it is referred to in the literature as lactase Phlorizinhydrolase. Structurally, the LCT gene of four similar domains, wherein the lactase activity in the fourth, and the Phlorizinhydrolase takes place in the third domain.

As an integral membrane protein localized in the brush border LPH the columnar cells of the arranged main Zottenepithels of the small intestine of all mammals. Mutations in the LCT gene may be the cause of hereditary variants of lactose intolerance through a reduction in LPH activity. On the other hand, certain other mutations cause an increase on LPH- production and their retention in adulthood Laktosepersistenz especially for residents of the northern hemisphere. The normal state, however, is a reduction in LPH- production after lactation.

Evolution

Due to the fourfold glycosidase -1 domain is assumed two Genverdopplungen in the evolution of the LCT gene. That the last of these duplications took place before the evolution of vertebrates, the fact it can be seen that already have orthologous to LCT genes in several species of fish four glycosidase - 1 domains.

For the evolution of Lactasepersistenz mutation selection in their milk -drinking cultures is the cause. The propagated by Beja - Pereira and other co-evolution with a similar mutation in dairy cows is now the most likely explanation for the high proportion of persistence in the human population and its distribution profile.

Biosynthesis

The gene encoding LPH gene LCT is located on the second chromosome ( 2q21 ). The LCT gene spans 17 exons and 49 340 base pairs. After transcription, the mRNA is produced which contains 6274 bases and is per - LPH ​​pre- translated into a 1927 amino acid long molecule. This contains four similar glycosidase 1 domains, and a signal sequence, that causes prepro LPH is transported to the cell membrane of the ER. After removal of the signal sequence (19 amino acids) cut peptidases the molecule into two parts: LPHß ( 1061 amino acids) and another protein LPHα (847 amino acids), which is probably necessary for the transport of LPHß dimer to the membrane, the last still phosphorylated and is glycosylated.

Catalyzed reaction

Lactose is split into glucose and galactose. The optimal conditions for the lactase are at a pH value of six, at a temperature of 25 ° C.

Industrial use

Commercially produced lactase derived from Kluyveromyces fragilis yeast like. The enzyme thus obtained is offered in the form of tablets and capsules, so that people with lactose intolerance can tolerate milk products themselves. Also, there are lactose-free milk wherein the lactose has been split by the addition of lactase; so is this milk for human consumption, which lack the enzyme lactase.

In the manufacture of ice cream lactase is used, since the cleavage products of glucose and galactose are sweeter than lactose, and thus the sugar can be restricted. In addition, lactose crystallized at temperatures as they exist in the ice cream, while the fission products continue to be solved and give the ice so a finer texture.

Quantities are expressed in FCC units. 1000 FCC units can break down milk sugar 5 grams in optimal conditions. It depends, inter alia, on the viscosity of the solution. In viscous solutions, a larger amount of the enzyme is needed. Since milk is flocculated in the acidic environment of the stomach, it also has a larger amount lactase to break down the lactose requires completely if you take lactase to participate directly in the consumption of dairy products.