In this paper, a novel observation is made on a one-dimensional compressible Navier-Stokes model for the dynamic combustion of a reacting mixture of γ-law gases (γ > 1) with discontinuous Arrhenius reaction rate function, on both bounded and unbounded domains. We show that the mass fraction of the reactant (denoted as Z) satisfies a weighted gradient estimate Zy/ √ Z ∈ L ∞ t L 2 y , provided that at time zero the density is Lipschitz continuous and bounded strictly away from zero and infinity. Consequently, the graph of Z cannot form cusps or corners near the points where the reactant in the combustion process is completely depleted at any instant, and the entropy of Z is bounded from above. The key ingredient of the proof is a new estimate based on the Fisher information, first exploited by [2,7] with applications to PDEs in chemorepulsion and thermoelasticity. Along the way, we also establish a Lipschitz estimate for the density.