Both glyceraldehyde 3-phosphate and dihydroxyacetone phosphate are substrates for the enzyme triose phosphate isomerase. In a...

Both glyceraldehyde 3-phosphate and dihydroxyacetone phosphate are substrates for the enzyme triose phosphate isomerase. In a study by Knowles et al the k_M for glyceraldehyde 3-phosphate was determined to be 0.47mM with a Vmax of about 410 uM/min. Whereas, for the substrate dihydroxyacetone phosphate the k_M was determined to be 0.97 mM and the Vmax was about 41 uM/min. (Biochem J 129 (2) 1972:301-310). Triose phosphate isomerase has a relatively weak affinity for _______

A. glyceraldehyde 3-phosphate because the k_M is lower in comparison

B. dihydroxyacetone phosphate because the k_M is higher in comparison

C. glyceraldehyde 3-phosphate because the Vmax is higher in comparison

D. dihydroxyacetone phosphate because the Vmax is lower in comparison

Solutions

Expert Solution

Substrate (S) binds catalytic site of enzyme (E) to produce a enzyme-substrate (E-S) complex and eventually a product. This binding is mostly reversible and sometimes could be irreversible.

Enzyme is a catalyst so it is formed back in a reaction.

Talking about reaction rate, at the very beginning enzyme has a lot of availble catalytic sites. They accommodate the low levels substrate to facilitate the reaction.

As you increase the concentration of substrate, the catalytic sites get saturated with substrate and no more sites are available to bind. And you end up in excess substrate which could be utilized only when how fast the enzyme forms a product.

Here the substrate concentration is Km also called Michaleis-Menton constant. And the maximum rate when an enyme got saturated is Vmax. The relation between reaction rate and substraate concetration give is hyperbolic as shown below.

Km is the substrate concetration where the reaction rate is half-maximum i.e. 1/2 Vmax

An enzyme with high Km usually has low affinity for its substrate. Low Km indicate high affinity. Lower the Km faster the reaction and larger the Vmax.

So the answer for the abov question is

Triose phosphate isomerase has a relatively weak affinity for dihydroxyacetone phosphate because the Km is higher in comparison.

Answer is B

queen_honey_blossom answered 1 year ago

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