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We investigated the emission of K$\alpha$ iron line from the massivemolecular clouds in the Galactic center (GC). We assume that at present thetotal flux of this emission consists of time variable component generated byprimary X-ray photons ejected by Sagittarius A$^\ast$ (Sgr A$^\ast$) in thepast and a relatively weak quasi-stationary component excited by impact ofprotons which were generated by star accretion onto the central black hole. Thelevel of background emission was estimated from a rise of the 6.4 keV lineintensity in the direction of several molecular clouds, that we interpreted asa stage when the X-ray front ejected by Sgr A$^\ast$ entered into these clouds.The 6.4 keV emission before this intensity jump we interpreted as emissiongenerated by subrelativistic cosmic rays there. The cross-section of K$\alpha$vacancies produced by protons differs from that of electrons or X-rays.Therefore, we expect that this processes can be distinguished from the analysisof the equivalent width of the iron line and time variations of the width canbe predicted. The line intensity from the clouds depends on their distance fromSgr A$^\ast$ and the coefficient of spacial diffusion near the Galactic center.We expect that in a few years the line intensity for the cloud G\,0.11$-$0.11which is relatively close to Sgr A$^\ast$ will decreases to the level$\lesssim$ 10% from its present value. For the cloud Sagittarius B2 (Sgr B2)the situation is more intricate. If the diffusion coefficient $D\gtrsim10^{27}$ cm$^2$ s$^{-1}$ then the expected stationary flux should be about 10%of its level in 2000. In the opposite case the line intensity from Sgr B2should drop down to zero because the protons do not reach the cloud.

K-shell Emission of Neutral Iron Line from Sgr B2 Excited by Subrelativistic Protons