Fructose-bisphosphate aldolase (), often just aldolase, is an enzyme catalyzing a reversible reaction that splits the aldol, fructose 1,6-bisphosphate, into the triose phosphates dihydroxyacetone phosphate (DHAP) and glyceraldehyde 3-phosphate (G3P). Aldolase can also produce DHAP from other (3S,4R)-ketose 1-phosphates such as fructose 1-phosphate and sedoheptulose 1,7-bisphosphate. Gluconeogenesis and the Calvin cycle, which are anabolism, use the reverse reaction. Glycolysis, a catabolism, uses the forward reaction. Aldolase is divided into two classes by mechanism.
The word aldolase also refers, more generally, to an enzyme that performs an aldol reaction (creating an aldol) or its reverse (cleaving an aldol), such as Sialic acid aldolase, which forms sialic acid. See the list of aldolases.
Mechanism and structure
The of both classes each have an Protein domain folded into a TIM barrel containing the active site. Several subunits are assembled into the complete protein. The two classes share little sequence identity.
With few exceptions only class I proteins have been found in , land plant, and green algae. With few exceptions only class II proteins have been found in fungi. Both classes have been found widely in other and in bacteria.Trung Hieu Pham, Shreesha Rao, Ta-Chih Cheng, Pei-Chi Wang, Shih-Chu Chen,
The moonlighting protein fructose 1,6-bisphosphate aldolase as a potential vaccine candidate against Photobacterium damselae subsp. piscicida in Asian sea bass (Lates calcarifer),
Three forms of class I protein are found in .
Aldolase A is preferentially gene expression in muscle and brain; aldolase B in liver, kidney, and in ; and aldolase C in brain. Aldolases A and C are mainly involved in glycolysis, while aldolase B is involved in both glycolysis and gluconeogenesis. Some defects in aldolase B cause hereditary fructose intolerance. The metabolism of free fructose in liver exploits the ability of aldolase B to use fructose 1-phosphate as a Enzyme substrate. Archaeal fructose-bisphosphate aldolase/phosphatase is presumably involved in gluconeogenesis because its product is fructose 6-phosphate.
and also
Aldolase is used in the reversible trunk of gluconeogenesis/glycolysis
Aldolase is also used in the part of the Calvin cycle shared with gluconeogenesis, with the irreversible phosphate hydrolysis at the end catalyzed by fructose 1,6-bisphosphatase
In gluconeogenesis 3-PG is produced by enolase and phosphoglycerate mutase acting in series
In the Calvin cycle 3-PG is produced by RuBisCO
G3P is produced by phosphoglycerate kinase acting in series with glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in gluconeogenesis, and in series with glyceraldehyde-3-phosphate dehydrogenase (NADP+) (phosphorylating) in the Calvin cycle
Triose-phosphate isomerase maintains DHAP and G3P in near equilibrium, producing the mixture called triose phosphate (TP)
Thus both DHAP and G3P are available to aldolase.
/ref> The two classes are often present together in the same organism. Plants and algae have aldolase, sometimes a relic of endosymbiosis, in addition to the usual cytosolic aldolase. A bifunctional fructose-bisphosphate aldolase/phosphatase, with class I mechanism, has been found widely in archaea and in some bacteria. The active site of this archaeal aldolase is also in a TIM barrel.
In gluconeogenesis and glycolysis
In the Calvin cycle
Reactions
Moonlighting properties
Further reading
External links
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