  Bezrukavnikov-Finkelberg-Mirkovi\'c [Compos. Math. {\bf 141} (2005)]
identified the equivariant $K$-group of an affine Grassmannian, that we refer
as (the coordinate ring of) a BFM space \'a l\`a Teleman [Proc. ICM Seoul
(2014)], with a version of Toda lattice. We give a new system of generators and
relations of a certain localization of this space, that can be seen as a
version of its Darboux coordinate. This establishes a conjecture in
Finkelberg-Tymbaliuk [Progress in Math. {\bf 300} (2019)] that relates the BFM
space of a connected reductive algebraic group with those of Levi subgroups.
