Aldolases

Generic name for many close enzymes (EC 4.1.2)

D-fructose bifosfate aldolase (EC 4.1.2.13) catalyzes the cleavage of fructose-1,6-diphosphate into two triose phosphates: glyceraldehyde-3-phosphate and dihydroxyacetone phosphate. It is a reversible reaction, with the equilibrium favoring the formation of fructose-1,6-diphosphate rather than its cleavage.

Fructose-1,6-diphosphate dihydroxyacetone phosphate + glyceraldehyde-3-phosphate

Fructose-1,6-diphosphate cleaves only because the reaction products are used in later reactions without accumulating in the cytoplasm. Aldolase is a well-studied enzyme with a tetrameric structure. Its molecular mass is about 10 kDa. Aldolase is most active in neutral or weakly alkaline conditions. Its active site contains a lysine residue that reacts with the ketone group of fructose-1,6-diphosphate. At least three aldolase isomers are found in human and animal tissues.

Aldolase A is produced in erythrocytes, muscles, and fibroblasts. The study of aldolase A is used to diagnose and monitor muscle injuries. It increases in Duchenne-Becker muscular dystrophy, dermatomyositis, polymyositis, and trichinosis. Its concentration in the blood remains unchanged in cases of neural injuries and multiple sclerosis.

Aldolase B is most commonly produced in the liver, kidneys, and small intestines. Liver cells lack enzymes that convert fructose-1-phosphate to fructose-6-phosphate, so it is cleaved by the enzyme aldolase B.

Aldolase B cleaves D-fructose-1-P, therefore, the fructose metabolism in liver cells does not require the enzyme phosphofructokinase, which limits the activity of the glycolysis process. Thus, fructose breakdown in the liver is much faster than in other tissues. Aldolase B is active in the kidneys and small intestines.

Source | Glossary of Most Commonly Used Biomedical Terms and Concepts | Lithuanian University of Health Sciences | Academician Professor Antanas Praškevičius, Professor Laima Ivanovienė