def v_9(self, x):
        # Phosphoglycerate mutase
        # P3G <=> P2G
        return (self.VmPGM*(-(x[8]/self.KeqPGM) + x[9]))/(self.KmPGMP3G*(1 + x[8]/self.KmPGMP2G + x[9]/self.KmPGMP3G))