Question

Which of the following statements about allosteric modulators is true?

a) Positive heterotropic modulators bind to the active site
b) Negative heterotropic modulators bind to the active site
c) Positive modulators push the protein into the T-state
d) Negative modulators push the protein into the R-state
e) Positive & negative modulators change P50

Answer 1

Positive and negative allosteric modulators bind to sites other than the active site on an enzyme, affecting its activity by altering the enzyme's conformation and, consequently, the active site's affinity for the substrate.

Step-by-step explanation:

Regarding allosteric modulators, the true statement from the options provided is (e) Positive & negative modulators change P50. Allosteric modulators are compounds that bind to a site on an enzyme other than the active site, causing a conformational change that affects the enzyme's activity. Positive modulators enhance enzyme activity by increasing the affinity of the enzyme's active site for the substrate, shifting the protein into the more active 'R-state'. Conversely, negative modulators decrease enzyme activity by reducing the active site's affinity for the substrate, shifting the protein into the less active 'T-state'.

Specific examples include phosphofructokinase, where AMP and ADP act as positive modulators, while ATP and citrate function as negative modulators. It's important to note that neither positive nor negative heterotropic modulators bind to the active site; they bind to separate allosteric sites, influencing the protein's structure and function from a distance.