  We present a parametrization of the chiral even generalized parton
distributions, $H$, $E$, $\widetilde{H}$, $\widetilde{E}$, for the quark,
antiquark and gluon, in the perturbative QCD-parton framework. Parametric
analytic forms are given as a function of two equivalent sets of variables
$x,\xi,t$ (symmetric frame) and $X,\zeta,t$ (asymmetric frame), at an initial
scale, $Q_o^2$. In the $X>\zeta$ region a convenient and flexible form is
obtained as the product of a Regge term $\propto X^{-\alpha + \alpha' t}$,
describing the low $X$ behavior, times a spectator model-based functional form
depending on various mass parameters; the behavior at $X<\zeta$, is determined
using the generalized parton distributions symmetry and polynomiality
properties. The parameters are constrained using data on the flavor separated
nucleon electromagnetic elastic form factors, the axial and pseudoscalar
nucleon form factors, and the parton distribution functions from both the deep
inelastic unpolarized and polarized nucleon structure functions. For the gluon
distributions we use, in particular, constraints provided by recent lattice QCD
moments calculations. The parametrization's kinematical range of validity is:
$0.0001 \leq X \leq 0.85$, $0.01 \leq \zeta \leq 0.85$, $0 \leq -t \leq 1$
GeV$^2$, $2 \leq Q^2 \leq 100$ GeV$^2$. With the simultaneous description of
the quark, anti-quark and gluon sectors, this parametrization represents a
first tool enabling a global QCD analysis of deeply virtual exclusive
experiments.
