Ming Fa minfa at PANTHER.CMB.UMU.SE
Thu Apr 18 11:25:13 EST 1996

Hello, everyone!

I have a protein with only two cysteines. I would like to label 
these cysteins with spin-label probe to measure the distance 
between these two residues. I got the probe called 4-(2-Iodoacetamide)-TEMPO
My questions are:

1. How to detect the efficiency of incorparation of the probe to protein.

2. Do I need 100% labeling (both -SH groups in cysteines are 
   coupled to spin probe in one molecule). Will single-labeled
   protein (only one cysteine is on) effect EPR spectrum to 
   deviate the distance measurement.

Looking forward to getting the advice from experts. Thank you in

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