The Use of Molybdic Acid as a Precipitant for Blood Proteins

During the many years that tungstic acid has been employed as a precipitant for blood proteins, as suggested by Folin and Wu, the method has met with practically no criticism and has probably been one of the most widely employed processes used in biochemistry. It is, however, well to have more than a single method of procedure available in connection with special problems which may arise, so we feel that in spite of the wide-spread acceptance of tungstic acid as a protein precipitant, many will find the use of molybdic acid valuable at times as an alternative procedure. While tungstic acid has been found to leave unaffected the generally recognized non-protein constituents of the blood, we have already reported (1) that in the case of thioneine (ergothioneine) there is a marked loss following precipitation with tungstic acid. Recently Eagles and Vars (2) have reported a loss of thioneine where blood is precipitated with any of the ordinary protein precipitants. At one time we encountered a sample of tungstate which led to no precipitation of thioneine. The J. T. Baker Company, which cooperated with us in this matter, has not been able to duplicate the particular sample which behaved so peculiarly in this respect.*