  The paper deals with a next-to-leading order analysis of the radiative $B \to
K^* \gamma$ decay. Working in a PQCD approach, we compute the correction to the
essential form factor, coming from a single gluon exchange with the spectator.
We investigate the supersymmetry effects on the branching ratio and direct CP
asymmetry and constrain the squark mixing parameter $(\delta_{23}^d)_{LR}$.
