Several answers were received to this query. I'm not sure I have the definitive solution yet, but I am a little further advanced- Calman Prussin said- >In my experience all FITCs (and PEs) are equal, however all >fluoresceins are not equal. > >The MolProbes catalog lists the conjugate as "fluorescein labeled >dextran", not FITC. My guess is they used FSX, fluorescein-x >succinimidyl ester, which has a longer wavelength emission and hence >requires more compensation. Dave Coder said- >Also relevant, is the observation of the effect of emission difference on >compensation that Joe Trotter illustrated some time back. See the >FITC/Fluorescein Alert! at: > >http://facs.scripps.edu/cd4fitc.html Thanks for these pointers. It was sloppy of me not to have noted that I was using fluorescein dextran, some in the lab routinely refer to it as FITC dextran. However, I hadn't appreciated the difference in emission spectra between FITC and fluorescein, so I have learnt something. Nevertheless, I noted a similar problem using an out-of-date conjugated sheep anti-mouse, and I have checked- it is definitely a FITC conjugate. As I said, it seems to stain the cells brightly enough and gives a good FL1 signal, but also emits strongly in FL2. Is this a known effect of deterioration of FITC conjugates over time? ______________________________________________ Dr William Smith Institute for Child Health Research (Company Limited by Guarantee ACN 009 278 755) Subiaco, Western Australia, 6008 PO Box 855 West Perth WA 6872 Ph 61 8 9340 8792/8388, Fax 61 8 9388 3414 email williams@ichr.uwa.edu.au ______________________________________________
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