In a recent study published in Langmuir, Mandal and Sen claim to propose a “new” kinetic model to analyze the directional movement of enzyme molecules in response to a gradient of their substrate, with the supposedly new prediction that net movement occurs up the substrate gradient when the diffusivity of the substrate-bound enzyme is lower than that of the unbound enzyme and movement occurs down the substrate gradient when the diffusivity of the substrate-bound enzyme is higher than that of the unbound enzyme. In this Comment, we point out that the same result and prediction (with an identical derivation) were already obtained by us as one of the central results in ref, whose abstract indeed states that we found “a new type of [chemotactic] mechanism due to binding-induced changes in the diffusion coefficient of the enzyme” which “points toward lower substrate concentration if the substrate enhances enzyme diffusion and toward higher substrate concentration if the substrate inhibits enzyme diffusion.”