Googling peg polydispersity returns this as the second hit http://www.springerlink.com/content/tp643l7678048447/
which is circa 1973 data from behind the iron curtain. The technology may have improved, and the most recent I can quickly find is this paper Plata et al., Electrophoresis, (2010), 31:679 Seems like PEG1000 would have anywhere between 15-30 monomers. Cheers, Ed. On Thu, 2010-08-12 at 20:30 +0000, MARTYN SYMMONS wrote: > That's a good point, Ed > > Based on the formula: HO CH2-(CH2-O-CH2)n-CH2OH, PEG MW = 44n+62, a table of > n to MW goes like below which gives an idea of what range is possible. > Someone maybe knows what polydispersity can be expected from the synthetic > process. As you say though, a specific range could partition out of the bulk > to the protein surface. And the main point of the original post was that only > a subset of atoms in the bound PEG may be ordered enough to see. > n MW > 5, 282. > 6, 326. > 7, 370. > 8, 414. > 9, 458. > 10, 502. > 11, 546. > 12, 590. > 13, 634. > 14, 678. > 15, 722. > 16, 766. > 17, 810. > 18, 854. > 19, 898. > 20, 942. > 21, 986. > 22, 1030. > 23, 1074. > 24, 1118. > 25, 1162. > 26, 1206. > 27, 1250. > 28, 1294. > 29, 1338. > 30, 1382. > 31, 1426. > 32, 1470. > 33, 1514. > 34, 1558. > 35, 1602. > 36, 1646. > 37, 1690. > 38, 1734. > 39, 1778. > 40, 1822. > 41, 1866. > 42, 1910. > 43, 1954. > 44, 1998. > 45, 2042. > 46, 2086. > 47, 2130. > > > > --- On Thu, 12/8/10, Ed Pozharski <epozh...@umaryland.edu> wrote: > > > From: Ed Pozharski <epozh...@umaryland.edu> > > Subject: Re: [ccp4bb] PEG in the pdb? > > To: CCP4BB@JISCMAIL.AC.UK > > Date: Thursday, 12 August, 2010, 17:35 > > PEG solutions contain fragments of > > all sizes - it is the average size > > (however defined by the manufacturer) that is 1000. > > So technically it > > is incorrect to claim that you have PEG1000 molecules bound > > to your > > protein, it is most likely much shorter fragments that can > > penetrate the > > channels in protein crystals. > > > > It's not a lot of work to generate monomer libraries for > > peg fragments > > of different length (and some are available from standard > > monomer > > libs). > > > > I always wondered why PEG is not defined in the standard > > libraries as a > > polymer - perhaps because it is rarely needed. Or is > > it? > > > > Ed. > > > > On Thu, 2010-08-12 at 08:16 +0000, Klaus Sengstack wrote: > > > Hi everybody, > > > > > > I just solved the structures of an enzyme an some > > variants. In the > > > active site cavity of each variant I found one or two > > fragments of > > > PEG1000 bound. I used PEG1000 in the crystallization > > condition. Among > > > the enzyme variants the number of non-hydrogen atoms > > of these PEG > > > fragments varies between 7 and 19 atoms. Now I want to > > deposit the > > > structures in the pdb and my question is, if I have to > > define each > > > fragment as a single ligand (what would be a lot of > > work) or can I > > > define them as PEG1000 molecules? Thanks. > > > > > > K.S. > > > > > > > > > > -- > > "I'd jump in myself, if I weren't so good at whistling." > > > > > > Julian, King of Lemurs > > > -- Edwin Pozharski, PhD, Assistant Professor University of Maryland, Baltimore ---------------------------------------------- When the Way is forgotten duty and justice appear; Then knowledge and wisdom are born along with hypocrisy. When harmonious relationships dissolve then respect and devotion arise; When a nation falls to chaos then loyalty and patriotism are born. ------------------------------ / Lao Tse /
