Dependence of Deep Inelastic Structure Functions on Quark Masses

We argue that the difference between the structure functions corresponding to deep inelastic scattering with and without heavy quarks in the current fragmentation region scales at high $Q^2$ and fixed (low) $x_{Bj}$. The lower bound on charm contribution to the total structure function, $F_2^c(Q^2,x)$, is calculated and compared with the recent data on $F_2^c(Q^2,x)$ from H1 Collaboration.