What conclusion can be drawn concerning an inhibitor if the Km is the same in the presence and absence of the inhibitor

The inhibitor has a structure that is not similar to the substrate.

Explanation:

Enzymes are molecules that act as catalysts of chemical reactions, accelerating the reaction rate without affecting the equilibrium of the reaction, as long as it is energetically possible. They act on molecules called substrates, which are converted into different molecules called products.  

Enzymes are very selective with their substrates and are also susceptible to inhibitors which are molecules that regulate enzyme activity, inhibiting its activity. Inhibitors can be classified as reversible and irreversible. Irreversible inhibitors bind covalently to the enzyme with no possibility of reversing the modification they make, while reversible inhibitors bind reversibly to the enzyme and can reverse the modification.

A reaction occurring under the control of an enzyme reaches equilibrium much faster than the corresponding uncatalyzed reaction. The reaction, i.e. the production of products, can reach a saturation point if the substrate concentration increases too much, decreasing the concentration of free enzyme, which becomes the form with bound substrate. At the maximum rate (Vmax) of the enzyme, all active sites of the enzyme have substrate bound, and the amount of complexes is equal to the total amount of enzyme. The amount of substrate required to obtain a given reaction rate is also important and this parameter is given by the Michaelis-Menten constant (Km), which is the concentration of substrate required for an enzyme to reach half its maximum velocity. Each enzyme has a characteristic Km value for a given substrate, which can tell us how close the binding between the substrate and the enzyme is. Then, inhibitors bind to the substrate and increase the Km value as it interferes with the binding between substrate and enzyme. In this case, the Km value of the enzyme is the same in the presence and absence of the inhibitor, this means that there is no change, because the inhibitor has a different structure to the substrate, it does not bind and does not change the Km value.

is in the form atp or adenosine triphosphate