Question

Which of the following must be true of enzymes that are regulated allosterically?

1) The enzyme must have at least one domain or subunit that binds to the regulatory compound, and at least one catalytic domain or subunit.
2) The enzyme must never catalyze the reverse reaction.
3) The allosteric regulator may bind to the active site.
4) The enzyme must be part of a biosynthetic pathway (such as one that synthesizes the amino acid tryptophan).

Answer 1

Enzymes that are regulated allosterically must have both a regulatory and catalytic component. Allosteric regulation involves the binding of a regulator molecule to an allosteric site on the enzyme, inducing a conformational change in the enzyme's active site. This impacts substrate binding and reaction rates.

Step-by-step explanation:

Enzymes that are regulated allosterically must have at least one domain or subunit that binds to the regulatory compound, and at least one catalytic domain or subunit. This is because allosteric regulation involves the binding of a regulator molecule to an allosteric site on the enzyme, which induces a conformational change in the enzyme's active site, impacting substrate binding and reaction rates. Therefore, for regulation to occur, the enzyme must have both the regulatory and catalytic components.

As for the other options:

1. The enzyme may catalyze the reverse reaction, as allosteric regulation can affect the forward and reverse reactions equally.
2. The allosteric regulator typically does not bind to the active site. Instead, it binds to an allosteric site, causing a conformational change in the enzyme and affecting substrate binding.
3. The enzyme does not need to be part of a specific biosynthetic pathway to be regulated allosterically. Allosteric regulation can occur in various metabolic pathways.