Question

Enzyme aldolase which helps in combining dihydroxyacetone phosphate with glyceraldehyde phosphate belongs to the category of
A. Ligases
B. Hydrolases
C. Transferases
D. Lyases

Answer 1

Hint: Aldolases is an important enzyme in the conversion of glucose into energy.
Also known as fructose-bisphosphate aldolase (ALD), it helps in catalyzing a reversible reaction that splits aldol, fructose 1,6-bisphosphate, into the triose phosphates dihydroxyacetone phosphate (DHAP) and glyceraldehyde 3-phosphate (G3P).

Complete Answer:
- Aldolase is present in all animal and plant tissue and most microorganisms. The Class I enzyme has three types: A, B, and C. Aldolase A is present in the developing embryo and an even higher amount is found in adult muscles.
- Type B, in the liver and kidney and Type C (along with some A) is found in the brain. Aldolases A and C are mainly involved in glycolysis whereas aldolase B is involved in both glycolysis and gluconeogenesis.
- The three isozymes (A, B, and C) are composed of four identical subunits, each a polypeptide chain of 360 amino acids. The enzyme has a homotetrameric structure with subunits that are approximately 40 kDa.
- The structure of these subunits is a beta-barrel, surrounded by alpha-helices and connecting loops. If activity of one of the four subunits of the homotetramer is knocked out, the entire complex is incapable of normal function, indicating a tight communication between active sites. Aldolases belong to the class Lyases.
- Lyases are enzymes that catalyze the breaking of C-C, C-O, C-N, C-S and other bonds by means other than hydrolysis or oxidation. These bonds are cleaved by the process of elimination and the result is the formation of a double bond or a new ring, or adding groups to double bonds. Example, Aldolases catalyzes the removal of aldehydes by elimination reactions.

Hence the correct option is Option D, ‘Lyases’.

Note: High aldolase levels are found in the blood when there is damage to the muscles or liver. During heart attacks or cirrhosis this damage can occur and earlier, an aldolase test was used to check this. Low aldolase levels can be seen in people with fructose intolerance, muscle-wasting disease and late muscular dystrophy.