Question

Which of the following is the sequence of steps followed by biotin-dependent enzymes, as listed below?

1) I. Transfer of the carboxyl group from carboxybiotin to the substrate
2) II. Activation of bicarbonate by ATP
3) III. Formation of carboxybiotin

Answer 1

The correct sequence for the steps undertaken by biotin-dependent enzymes is: (1) activation of bicarbonate by ATP, (2) formation of carboxybiotin, and (3) transfer of the carboxyl group to the substrate.

Step-by-step explanation:

The sequence of steps followed by biotin-dependent enzymes in carboxylation reactions is as follows:

1. Activation of bicarbonate by ATP
2. Formation of carboxybiotin
3. Transfer of the carboxyl group from carboxybiotin to the substrate

This process begins with the activation of bicarbonate where ATP is used to activate the bicarbonate (HCO3-), with the presence of Mg2+ to decrease the overall negative charge. Subsequently, the formation of carboxybiotin occurs through a nucleophilic attack of the biotin moiety on the activated carbonate, leading to the creation of carboxybiotin. Finally, the transfer of the carboxyl group from carboxybiotin to the substrate takes place, which enables the carboxyl group to be joined to the substrate, such as acetyl-CoA, completing the carboxylation process.