  We calculate the massive polarized three-loop pure singlet operator matrix
element $A_{Qq}^{(3), \rm PS}$ in the single mass case in the Larin scheme.
This operator matrix element contributes to the massive polarized three-loop
Wilson coefficient $H_{Qq}^{(3),\rm PS}$ in deep-inelastic scattering and
constitutes a three-loop transition matrix element in the variable flavor
number scheme. We provide analytic results in Mellin $N$ and in $x$ space and
study the behaviour of this operator matrix element in the region of small and
large values of the Bjorken variable $x$.
