From: Richard M Thomas <rthomas@ifp.mat.ethz.ch>
  To  : RASMB@bbri.harvard.edu
  Date: Thu, 24 Sep 1998 12:15:40 +0200

metals and vbar

Funny you should ask! I've spent this morning playing with some new density
data on a zinc metallothionein. This protein has only 68 amino acid
residues but 7 zinc atoms. At protein concentrations of 10-20mg/ml I get a
measured vbar of 0.648-0.655 ml/g. Assuming the tabulated value of the
density of zinc (7.14) and using the mass fraction contributions of the
zinc and (calculated, Sednterp) protein vbar I get a predicted value of
(wait for it) 0.65 ml/g.
This calculation seems reasonable but presumably makes a variety of
assumptions about the state of the metal atoms and their coordination. 
I don't know if this helps, and I would also be interested in the general
opinion.
Just to risk it - we are currently replacing the zinc atoms in the protein
with Cadmium and will re-attempt the vbar measurement next week. The
calculated value for this variant on the above basis is 0.626ml/g. Anyone
taking bets?
Regards to all
Richard

Dr Richard M Thomas
Inst. für Polymere
ETH-Zentrum
CH-8092 Zürich
Switzerland
(tel) +41 1 632 5540
(fax) +41 1 632 1073