and chilled in a
freezer for at least 30 min until they were frozen. The cells were then thawed and
transferred to a 1.5-ml Eppendorf tube. About 0.3 g of acid-treated glass beads
and 150 ml of 0.1 M 2-mercaptoethanol were added to the cells, which were then
disrupted by vortexing. The resulting cell extracts were assayed for XR and XDH
activities as described by Bolen and Detroy (5) and for XK activity as described