Boopathi

We are characterizing the Beta-Galactosidase from a hot spring bacteria. While assaying for B-Galactosidase using o-Nitrophenol Galactopyranoside we found that it also has Glucosidase activity. I looked for Glucosidase substrate and found that p-Nitrophenol Glucopyranoside is the commonly used substrate for B-Glucosidase. I want to check the Km and Vmax for both the substrates. But I could not find both of the substrate either with o-nitrophenol or p-nitrophenol. If I want to compare the enzyme actvity do I need to use the similar substrate or I can use different substrate, kindly clarify me....