The conditions in the drop play a huge role in the success of iodination. If you see iodinated histidines, this means that you had high pH - higher than 8 at least, as histidines are much harder to iodinate than tyrosines (which will work even at pH 5, and definitely at 6).
Paul's classic experiment is very nice :) If you're into even more classic experiments, check out: INACTIVATION OF PEPSIN BY IODINE AND THE ISOLATION OF DIIODO-TYROSINE FROM IODINATED PEPSIN ROGER M. HERRIOTT, 1936 http://www.pubmedcentral.nih.gov/picrender.fcgi?artid=2141501&blobtype=pdf The heavily modified method that I will be posting shortly does not involve adding iodine directly to the crystals, which is its sole (but I think significant) benefit :) Artem > Hi everyone, > the in situ iodination reaction described in the following classic paper > by > the late Paul Sigler works quite well. > > Iodination of a single tyrosine in crystals of alpha-chymotrypsin. > Sigler PB. > Biochemistry. 1970 Sep 1;9(18):3609-17. > > The primary purpose of my experiment (which took place 11 years ago > according to my notebook) was indeed to iodinate tyrosines, but difference > fourier analysis using calculated phases from the final refined MIR > structure to reveal the complete iodination model (out of curiosity), > showed > that in addition to iodination of two tyrosines, two histidines had also > been iodinated! In retrospect, I had actually run across those peaks in my > cross-difference fourier maps but thought that they were too 'secondary' > to > be included in the heavy atom model. > > Best wishes > Savas > > ---- > Savvas Savvides > L-ProBE, Unit for Structural Biology > Ghent University > K.L. Ledeganckstraat 35 > 9000 Ghent, BELGIUM > office: +32-(0)9-264.51.24 ; mobile: +32-(0)472-92.85.19 > Email: savvas.savvi...@ugent.be > http://www.lprobe.ugent.be/xray.html > > > > -----Original Message----- > From: CCP4 bulletin board [mailto:ccp...@jiscmail.ac.uk] On Behalf Of > Alessandro Vannini > Sent: Tuesday, March 31, 2009 9:11 PM > To: CCP4BB@JISCMAIL.AC.UK > Subject: Re: [ccp4bb] Halide soaking > > Hi, > it worked very nice for me in 1 out of 1 case where I tried it :-). > Very well diffracting crystals (1.8 Ang), rather small protein 20 > kDa, 50 %solvent content, 1 mol/ASU. 20-30 s soak in 0.5 M NaBr > resulted in 6 nice ordered sites. > It was crucial for us to collect a 3 wavelength MAD data set. A SAD > data set (using just the peak, even if with high redundancy ) was not > enough to obtain traceable electron density map, even-though > one could distinguish clearly protein boundaries and solvent channels. > > Good luck > > Ale > > On 31 Mar 2009, at 18:19, tat cheung cheng wrote: > >> Hi all >> >> I am now trying to do bromide soaking, but i am not really sure does >> the bromide atom enter my crystal. So is there any signs that >> indicate the entry of bromide atom? e.g. does the space group, cell >> dimension change? or just nothing change, and the bromide atom just >> get in? >> Thanks very much. >> >> T.C. Cheng >> >> >> Yahoo!Ïã¸ÛÌṩ¾WÉÏ°²È«¹¥ÂÔ£¬½ÌÄãÈçºÎ·À¹ ºÚ¿Í! ÕÇ°Íù http://hk.pro >> mo.yahoo.com/security/ Á˽â¸ü¶à! > > > > > > E-mail message checked by Spyware Doctor (6.0.0.386) > Database version: 5.12080 > http://www.pctools.com/en/spyware-doctor-antivirus/ >
