The glycolytic enzyme, aldolase, and the proteolytic enzyme, chymotrypsin, catal

Question

The glycolytic enzyme, aldolase, and the proteolytic enzyme, chymotrypsin, catalyze the breaking of a covalent bond. One of these enzymes catalyzes a reversible reaction the other does not. One of these enzymes is regulated by an irreversible method the other is not.

Write the balanced net reaction for each of these enzymes and identify the reaction that is not reversible. Explain why it is irreversible.

Water is involved in both of these reactions, but it is in the net reaction of one of these enzyme-catalyzed reactions. Explain how water is used in both of these reactions, but appears in only one net reaction.

There are six classes of enzymes: oxidoreductases, transferases, hydrolases, lyases, isomerases and ligases. To which classes of enzymes do these proteins belong?

Both enzymes use amino acid side-chains as nucleophiles in the early steps of their mechanisms, what amino acids are used as these nucleophiles? What electrophile is each of these nucleophiles attacking in the early catalytic steps?

One of these enzymes is a zymogen that is irreversibly regulated and the other is not. Which enzyme is regulated this way and what is the irreversible form of regulation? Given the biological function of this enzyme, why does this type of regulation make sense?

Explanation / Answer

1,ALDOLASE is a key enzyme in the fourth step of glycolysis, as well as in the reverse pathway gluconeogenesis. It catalyzes the reversible conversion of fructose-1,6-bisphosphate to glyceraldehydes-3-phosphate and dihydroxyacetone phosphate by aldol cleavage of the C3–C4 bond. As a result, it is a crucial player in ATP biosynthesis. ALDOA also contributes to other "moonlighting" functions such as muscle maintenance, regulation of cell shape and motility, striated muscle contraction, actin cytoskeleton organization, .

2hymotrypsin is synthesized in the pancreas by protein biosynthesis as a precursor called chymotrypsinogen that is enzymatically inactive. On cleavage by trypsin into two parts that are still connected via an S-S bond, cleaved chymotrypsinogen molecules can activate each other by removing two small peptides in a trans-proteolysis. The resulting molecule is active chymotrypsin, a three-polypeptide molecule interconnected via disulfide bonds.

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