I am working on a protein complex which is activated by phosphate starvation conditions and ends up utilizing phosphonates or phosphites as phosphate sources in vivo. I have been able to purify the entire complex but it is not active. I was thinking of growing my cells (BL-21 DE3) in a phosphate starvation media supplementing it with a phosphonate source to see if that makes the complex active. I was wondering if anyone has any experience with making low or no phosphate media? Also, any suggestions about growing cells in the presence of substrates will be most welcome.