Studies on alcaptonuria

Abstract

The color which arises in the reaction of homogentisic acid with phosphomolybdic acid takes some time to develop to its maximum and the rate of color development depends on the concn. of homogentisic acid. The color develops more slowly with p-hydroxyphenylpyruvic acid but it is pointed out that the difference is not sufficient for a differential estimation. It is also shown that Beer''s law is only obeyed with lower concns. of homogentisic acid. The reaction is not very specific and has to be used with caution. Exptl. conditions for the iodometric estimation of homogentisic acid have been defined which give a recovery of about 99% in water and urine. Neither amino-acids such as glycine and cysteine nor keto acids like p-hydroxyphenylpyruvic acid interferes with the reaction. Hydroquinone and gentisic acid behave towards I like homogentisic acid, while catechol and dopa behave irregularly and might produce misleading results if present in significant amts. A new method for the estimation of homogentisic acid is described. The homogentisic acid is estimated by the reduction of Ag ions at pH 4.4; the Ag is precipitated in the form of a sol of small and fairly uniform particle size in the presence of a gold sol and gum arabic. The time curve of the color development is highly characteristic of the reducing compound used and permits a very specific estimation of homogentisic acid in the presence of other reducing substances.