Acetylhomocysteine thiolactone

Therapeutic Function Treatment of hepatic disorders Chemical Name 2-Acetamido-4-mercaptobutyric acid 7-lactone Common Name Acetylhomocystein thiolactone acetamido thiobutyrolactone Structural Formula o... 

Silver ion also catalyzes nucleophilic reactions of thiol esters, including reactions of acetylhomocysteine thiolactone (12) and diethylethylphosphonothiolate (52). In the first reaction, an insoluble complex of silver ion and the substrate was first produced at pH 7.5, which then reacted with the nucleophile, in this case an amino group of a protein. In the second reaction silver ion complexes of the substrate were also postulated, on the basis that silver ion complexes with sulfur are much more stable than those with oxygen (I). The complexes postulated were 1 1 and 2 1 silver ion-substrate complexes. These complexes were suggested to react with the nucleophiles, water and fluoride ion, giving as products phos-phonic acid and phosphonyl fluoride, respectively, and silver mercaptide. It is evident that the last reaction at least must involve only the direct interaction of a silver ion with the sulfur atom of the thiol ester without chelate formation. Therefore it appears the metal ion-catalyzed reactions of thiol esters are unique, in that they involve complex formation, but not chelate formation in their catalytic mechanism. 

Common Name Acetylhomocystein thiolactone Acetamido thiobutyrolactone... 

It may seem odd that the technique of spectrophotometric titration, so extensively applied to the tyrosyl residues of proteins, has not been used in the study of protein sulfhydryl groups. The only study of this sort known to the author is the determination of the ionization constant of —SH grouj of thiolated gelatin (introduced by reaction with A -acetylhomocysteine thiolactone). By measuring the change in absorptivity as a function of pH at 2380 A, Benesch and Benesch (1958) found the apparent acidity of the thiol groups of the modified gelatin (pK = 9.8) to be nearly the same as that of an appropriate model compound, A -acetylhomocysteine (pK = 10.0). 

However, one of the first matrices used for insolubilization of the aflBnant was cellulose that had been partially etherified with 3-hydroxy-phenoxy or 4-diazobenzyl groups (which react with diazotized protein or protein, respectively). Amino compounds may also be attached to the acid chlorides of carboxy polysaccharides.0-(3-Allyloxy-2-hydroxy-propyl)-cellulose and -Sephadex can be mercuriated and, in this form, used for isolation of thiolated antibodies and fractionation of mononucleotides according to their aflBnity for an organomercurial. Another mercurial, prepared by treatment of 0-(2-aminoethyl)Sephadex with IV-acetylhomocysteine thiolactone to give a thiol (49) which, on treatment with 2,5-bis[(acetoxymercuri) methyl]-1,4-dioxane, gives 50, can also be used in aflSnity chromatography of thiolated proteins. 

I FIGURE. 5.llmqc The 2-D HMQC NMRspectrum ofW-acetylhomocysteine thiolactone inCDCI3. 

I FIGURE 11.S.Amftf The 2-D HMBC NMR spectrum ofW-acetylhomocysteine thiolactone in CDCI3,... 

Species coupled to agarose cyclic imidocarbonate 2-Acetamido-2-deoxy-jS-D-glucopyranoside A-Acetylhomocysteine thiolactone... 

Albumins.—Albumin has been converted into a cortisol-succinyl derivative, an immobilized form of which was used for affinity chromatography. Bovine serum albumin has been polythiolated, by reaction with iV-acetylhomocysteine thiolactone, and then covalently coupled to cellulose xanthate to form an immobilized derivative. ... 

Several successful attempts have been made at introducing mercapto groups into proteins without degrading the polypeptide chain. N-acetylhomocysteine thiolactone (LIV) in the presence of silver ion reacted readily with the primary amino group of lysine residues to produce thiolated proteins (LV) (77). 

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