problem with isoelectric focussing on beta lactamases

[Poon Wai Mun]

dear netters,

we are doing a project on Beta-lactamases. Currently, we are using comassie
blue to stain for protein bands after isoelectric foccusing. However, there
were no protein bands shown but an activity stain showed bands for the
various samples we used. The same senario happened when we did a silver
stain. Can anybody please help us out. Thanks a zillions.

Regards 
Wai Mun

PS: the gel we use has a pI ranging from 3 to 9. The gel we use is obtained
from Pharmacia Biotech. The markers for IEF were clearly shown after
coomassie and silver staining.