CHRONOSIS is the deposition of a brown-0 black pigment in the connective tissues of patients with alcaptonuria. The essential feature of the alcaptonuria syndrome is the excess accumulation of homogentisic acid (HGA), resulting from a deficiency of the enzyme HGA oxidase, which, if present, would metabolize the HGA to maleylacetoacetic acid.l Ochronosis must then be the result of an alternate pathway of HGA metabolism, which ultimately is4 terminated as a melaninlike pigment, irreversibly bound to connective tissue components. Available data indicate that the production of this pigment probably involves the oxidation of HGA to benzoquinoneacetic acid (BQA) prior to the production of the polymerized product.2 Homogentisic acid or BQA, when injected intraperitoneally into guinea pigs, has a high affinity for albumin, skin, and ~artilage.~ However, BQA reacts chemically with proteins as contrasted to the physical binding of HGA with protein^.^ The investigation described in this paper presents an addition reaction that takes place between BQA and amino acids or other biological amines. Spectrophotometric and electrophoretic evidence obtained indicates that stable adducts were formed between the amines and BQA. The possible significance of this reaction in relation to the development of ochronosis is discussed.
MATERIALS AND METHODSAdducts of BQA and biological amines were prepared for absorption studies by adding 5.0 ml. of a solution containing 5 X 10-5 moles of HGA to 10 ml. of a solution containing 20 x 10-j moles of the amine in a small beaker containing a miniature magnetic stirring bar. The beaker was then placed on a magnetic stirrer, and a set of calomel glass electrodes was inserted into the solution connected to a Beckman model G pH meter. Dilute sodium hydroxide was added to obtain the desired pH. Unless stated otherwise, a pH of 8.0 was used to obtain the oxidation of HGA to BQA. Following the pH adjustment, the solution was stirred for 30 minutes and then diluted to 25 ml. with water. The reaction time was limited to 30 minutes so as to avoid interference by compounds other than BQA which could be formed in this mixture by a longer period of reaction and to have BQA as the primary quinone in the mixture. The absorbance of this solution was determined between 600 and 320 mp. This solution was further diluted 1:25 with water, and the absorption in the ultraviolet range was obtained. All spectrophotometric measurements were performed on a Beckman Model DU Spectrophotometer using 1.0 cm. Silica cells.Samples for electrophoresis studies were prepared by taking 2 X 10-4 moles of the amine and 1 X 10-4 moles of the HGA and dissolving them in 1.0 ml. of 5% sodium bicarbonate contained in a 15 X 125 mm. test tube. These solutions were mixed several times during a 30 minute interval on a Vortex mixer. Solutions containing the HGA alone and the corresponding amine alone were also prepared in an identical manner. Samples of each were spotted in the center of a 6 X 12 inch Whatman #42 filter paper, which had beeh s...
