  We generalize a theorem of Kapranov by showing that the Hall algebra of the
category of coherent sheaves on a weighted projective line (over a finite
field) provides a realization of the (quantized) enveloping algebra of a
certain nilpotent subalgebra of the affinization of the correponding Kac-Moody
algebra. In particular this yieds a geometric realization of the quantized
enveloping algebra of 2-toroidal (or elliptic) algebras of types D_4, E_6, E_7
or E_8 in terms of weighted projective lines of genus one.
