Methods for the Quantitative Determination of SH and S—S Groups in Proteins
Various methods of determining SH groups in proteins have been proposed, based on the numerous reactions in which these groups take part. A detailed description of these methods is given in a number of reviews (Chinard and Hellerman, 1954; Cecil and McPhee, 1959; Benesch and Benesch, 1962; Leach, 1966). We will limit ourselves to describing the most commonly used and the most exact methods, and also the methods put forward in the last few years and so not mentioned in these reviews. Some of the methods once used to determine SH groups (including those based on the use of nitroprusside, ferricyanide, iodine, and porphyrindin) are hardly used at all now, because they have insufficient specificity, or comparatively low sensitivity, or both. The reagents now most often used for the quantitative determination of protein SH groups are (a) mercaptide-forming compounds, (b) alkylating reagents, and (c) disulfides; recently the use of sulfenyl halides has also been proposed for this purpose.
KeywordsCysteic Acid Spectrophotometric Titration Silver Sulfide Mixed Disulfide Performic Acid
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