P-Chloromercuribenzoic acid

Submitted by Frank C. Whitmore and Gladys E. Woodward. Checked by Henry Gilman and J. D. Robinson. 

The chief impurity in the tolylmercuric chloride is mercurous chloride, which is converted to the oxide and remains in the manganese dioxide precipitate. 

In filtering the manganese dioxide from the strongly alkaline solution, it is best to support the filter paper by means of a cloth which is cut to fit the funnel and placed under the filter paper. 

It is necessary that the filtrate be cooled at least to 20° before acidifying to avoid the splitting of the C-Hg linkage. 

The caked acid loses water very slowly, even at iro°. Since the chief use of the acid is in preparing the p-halogen compounds, it need not be dried, but can be mixed with water while still wet. 

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Additional information <1> (<1> 1 mM p-chloromercuribenzoic acid or urea are no inhibitors, MphR(A) is a repressor protein that binds to the promoter of the mph(A) gene and negatively regulates the enzyme expression [3,10]) [3, 10]... 

CdBSl has not been extensively analysed but p-chloromercuribenzoic acid derivatisation yielded a peak on reverse phase HPLC corresponding to glutathione (A. Sewell, unpublished data). 

Abbreviations used TNBS = 2,4,6-trinitrobenzenesulfonic acid DTNB = 5,5 -dithiobis-(2-nitrobenzoic acid) 2-PDS = 2,2 -dipyridyl disulfide 4-PDS = 4,4 -dipyridyl disulfide CMB = p-chloromercuribenzoic acid. 

More recently, p-chloromercuribenzoic acid was used to eliminate the largely sulfhydryl reducing compounds present in extracts of animal tissues (04). Interfering substances, presumably glutathione, present in human erythroc)rtes were largely removed by this procedure. p-Chloro-... 

Finally, it is possible in unhydrolysed wool< ) to determine the free thiol groups by allowing the sample to react with Neohydrin, or with p-chloromercuribenzoic acid in a urea containing pH 7-8 5 buffer. In the determination of free S-S bonds the reaction... 

In the present section the preparation, purification, and analysis of p-chloromercuribenzoic acid are described a brief section on other mer-captide-forming agents is included. 

Preparation. The synthesis of p-chloromercuribenzoic acid is a simple procedure which requires no special apparatus. The procedure which follows is adapted from that of Whitmore and Woodward (145). The reaction is given in equation (17). 120 g. of NaOH is dissolved in 1.8 liters of distilled water in a 3-liter beaker equipped with a mechanical stirrer. 50 g. of p-tolylmercuric chloride... 

Of a series of conventional inhibitors tested with the bacterial enzyme, only p-chloromercuribenzoic acid caused significant loss of activity, and this was prevented by glutathione. The Neurospora enzyme was not affected by iodoacetate, A -phenylmaleimide, semicarbazide, or cyanide (Ottey and Tatum, 1956). It is noteworthy that neither inhibition nor activation studies gave any evidence for a metal cofactor in the Pseudomonas preparation. An enzyme from Nocardia that is also inhibited by organic mercury also showed no evidence for a metal component (Cain and Cartwright, 1960). An iron requirement has been found for the Neurospora enzyme, however. When sufficiently pure preparations are available, it will be of interest to analyze the other protocatechuic oxidases for bound metal. 

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