beta-galactosidase

[Mike Dyall-Smith]

        We have isolated a beta-galactosidase
-it cleaves X-gal and ONPG. The host bacterium
does not grow on lactose and lactose is not
expected in their normal environment. So our
question is: What is the best way to determine the
substrate specificity?? We are particularly interested
in what the natural substrate could be (whether it
is a catabolic or anabolic enzyme).