I wonder if anyone attempted to write a historic book on development of crystallography. That generation of crystallographers is leaving this world and soon nobody will be able to say how the protein and non-protein structures were solved in those days.
Alex On Jun 6, 2012, at 8:48 AM, Gerard Bricogne wrote: > Dear Fred, > > May I join Phil Evans in trying to dissipate the feeling that anomalous > differences were fictional before flash-freezing and all the mod cons. I can > remember cutting my teeth as a PhD student by helping Alan Wonacott with the > experimental phasing of his B.St. GAPDH structure in 1973-74. The data were > collected at room temperature on a rotating-anode source, using film on an > Arndt-Wonacott rotation camera (the original prototype!). The films were > scanned on a precursor of the Optronics scanner, and the intensities were > integrated and scaled with the early versions of the Rotavata and Agrovata > programs (mention of which should make many ccp4 old-timers swoon with > nostalgia). Even with such primitive techniques, I can remember an HgI4 > derivative in which you could safely refine the "anomalous occupancies" > (i.e. f" values) for the iodine atoms of the beautiful planar HgI3 anion to > 5 electrons. This contributed very substantially to the phasing of the > structure. > > In fact it would be a healthy exercise to RTFL (Read The Fascinating > Literature) in this area, in particular the beautiful 1966 papers by Brian > Matthews in Acta Cryst. vol 20, to see how seriously anomalous scattering > was already taken as a source of phase information in macromolecular > crystallography in the 1960's. > > In spite of that, of course, there would always be the unhappy cases > where the anomalous differences were too noisy, or the data processing > program too unsophisticated to filter them adequately, so that only the > isomorphous differences would be useful. It was in order to carry out such > filtering that Brian Matthews made another crucial contribution in the form > of the Local Scaling method (Acta Cryst. A31, 480-487). > > > With best wishes, > > Gerard. > > -- > On Wed, Jun 06, 2012 at 11:02:05AM -0400, Dyda wrote: >>> I suspect that pure MIR (without anomalous) was always a fiction. I doubt >>> that anyone has ever used it. Heavy atoms always give >>> an anomalous signal >> >>> Phil >> >> I suspect that there was a time when the anomalous signal in data sets was >> fictional. >> Before the invent of flash freezing, systematic errors due to decay and the >> need >> of scaling together many derivative data sets collected on multiple crystals >> could render >> weak anomalous signal useless. Therefore MIR was needed. Also, current >> hardware/software >> produces much better reduced data, so weak signals can become useful. >> >> Fred >> >> [32m******************************************************************************* >> Fred Dyda, Ph.D. Phone:301-402-4496 >> Laboratory of Molecular Biology Fax: 301-496-0201 >> DHHS/NIH/NIDDK e-mail:[email protected] >> Bldg. 5. Room 303 >> Bethesda, MD 20892-0560 URGENT message e-mail: [email protected] >> Google maps coords: 39.000597, -77.102102 >> http://www2.niddk.nih.gov/NIDDKLabs/IntramuralFaculty/DydaFred >> *******************************************************************************[m > > -- > > =============================================================== > * * > * Gerard Bricogne [email protected] * > * * > * Global Phasing Ltd. * > * Sheraton House, Castle Park Tel: +44-(0)1223-353033 * > * Cambridge CB3 0AX, UK Fax: +44-(0)1223-366889 * > * * > ===============================================================
