  The particle motion associated to the {\alpha}-relaxation in supercooled
liquids is still challenging scientists due to its difficulty to be probed
experimentally. By combining synchrotron techniques, we found the existence of
microscopic structure-dynamics relationships in Pt42.5Cu27Ni9.5P21 and
Pd42.5Cu27Ni9.5P21 liquids which allows us to disentangle structural and
kinetic contributions to the {\alpha}-process. While the two alloys show
similar kinetic fragilities, their structural fragilities differ and correlate
with the temperature dependence of the stretching parameter describing the
decay of the density fluctuations. This implies that the evolution of dynamical
heterogeneities in supercooled alloys is determined by the rigidity of the melt
structure. We find also that the atomic motion not only reflects the
topological order but also the chemical short-range order, which can lead to a
surprising slowdown of the {\alpha}-process at the mesoscopic length scale.
These results will contribute to the comprehension of the glass transition,
which is still missing.
