Aldolase

Aldolase

Aldolase is a kind of lyase, which in a narrow sense refers to an enzyme that catalyzes the reaction of cleaving 1.6-diphosphate-D-fructose to form 3-phosphate-D-glyceraldehyde with α-dihydroxyacetone phosphate (it can also be catalyzed in gluconeogenesis The reverse reaction of this reaction) refers to 1.6-diphosphate-D-fructose aldolas. (In a broad sense, it refers to enzymes that catalyze the same form of reaction. For example, rhamnose phosphate aldolase is also collectively called aldolase).

Figure 1. Protein structure of Aldolase.

Classifications

Aldolase is mainly divided into four kinds of dependence, namely acetaldehyde dependence, pyruvate/phosphoenolpyruvate dependence, glycine dependence and dihydroxyacetone phosphate dependence. The reaction is reversible aldol condensation, △G°'=5.73 kcal, is an important enzyme in the glycolysis of almost all living things. It has been purified from yeast and skeletal muscle. The standard sample from yeast can be inactivated by α, α′-bispyridine or cysteine, activated by Fe²⁺, Zn²⁺, Co²⁺, Cu²⁺, while the enzymes in muscle or plant tissues are not inhibited by dipyridine, etc. In skeletal muscle, this enzyme has a molecular weight of about 150,000 and is composed of 4 main subunits. In addition to the above reaction, aldolase also has the effect of condensing various aldehydes with dihydroxyacetone phosphate. Two types of aldolases have been found in nature. One type is in animal tissue, and the second type is mainly produced by bacteria and fungi. The first type of aldolase, in the presence of a substrate, is inhibited by sodium borohydride; the second type of aldolase is inhibited by EDTA.

Mechanism and structure

Class I proteins form protonated Schiff base intermediates, linking highly conserved active site lysine to DHAP carbonyl carbon. In addition, tyrosine residues play a vital role in stabilizing hydrogen receptors. Class II proteins use a different mechanism that can polarize carbonyl groups with divalent cations (such as Zn2+). The E. coli galactitol operon protein gatY and the N-acetylgalactosamine operon protein agaY are tagatose-bisphosphate aldolases and are homologs of class II fructose-bisphosphate aldolases. The two histidine residues in the first half of these homologous sequences have been shown to bind zinc.

Clinical significance

Serum aldolase determination is mainly used to diagnose muscle and liver diseases.

(1) Muscular diseases: Serum aldolase activity of patients with muscular dystrophy and polymyositis is increased. Among the muscular dystrophy, the enzyme activity is highest in duchenne, limb-girdle type and distal type, and the shoulder-brachial type and ocular muscle type are only slightly elevated or normal. In general, aldolase activity decreases with age, and the enzyme activity increases most significantly during the active phase and before muscle wasting, so its determination is helpful for the diagnosis of this disease. Serum aldolase activity in patients with myocardial infarction is increased, generally peaking at the onset of chest pain 24 to 48 hours, the change law is the same as AST, but earlier than AST. Angina is normal.

(2) Liver disease: The rise and fall of the activity of acute viral hepatitis aldolase is parallel to ALT. Chronic hepatitis, cirrhosis, and obstructive jaundice only increased slightly.

Reference