  As was discovered recently, 5-loop perturbative quenched QED approximation to
the QED $\beta$-function consist from the rational term and the term
proportional to $\zeta(3)$-function. It is stressed, that this feature is also
manifesting itself in the conformal invariant pqQED series for the 4-loop
approximation to the anomalous mass dimension. The 4-loop pqQED expression for
the singlet contribution into the Ellis-Jaffe polarized sum rule is obtained.
It coincides with the similar approximation for the non-singlet coefficient
function of Ellis-Jaffe sum rule and of Bjorken polarized sum rule. It is
stressed that this property is valid in all orders of perturbation theory
thanks to the conformal symmetry of pqQED series and to Crewther relation,
which relates non-singlet and singlet coefficient functions of Ellis-Jaffe sum
rule with the coefficient functions of non-singlet and singlet Adler
D-functions. The basic steps of derivation of Crewther relation in the singlet
channel from the AVV triangle diagram are outlined. The similarities between
analytical structure of asymptotic series for the coefficient functions in
pqQED and for the anomalous dimensions in N=4 conformal invariant
supersymmetric Yang-Mills theory are observed. The guess is proposed that the
appearance of $\zeta(3)$-terms in the pqQED expressions and the absence of
$\zeta(5)$-terms at the same level is the indication of absence of "wrapping"
interactions in pqQED.
