An inborn error of amino acid metabolism resulting from a defect in the enzyme HOMOGENTISATE 1,2-DIOXYGENASE, an enzyme involved in the breakdown of PHENYLALANINE and TYROSINE. It is characterized by accumulation of HOMOGENTISIC ACID in the urine, OCHRONOSIS in various tissues, and ARTHRITIS.

A mononuclear Fe(II)-dependent oxygenase, this enzyme catalyzes the conversion of homogentisate to 4-maleylacetoacetate, the third step in the pathway for the catabolism of TYROSINE. Deficiency in the enzyme causes ALKAPTONURIA, an autosomal recessive disorder, characterized by homogentisic aciduria, OCHRONOSIS and ARTHRITIS. This enzyme was formerly characterized as EC 1.13.1.5 and EC 1.99.2.5.

The yellowish discoloration of connective tissue due to deposition of HOMOGENTISIC ACID (a brown-black pigment). This is due to defects in the metabolism of PHENYLALANINE and TYROSINE. Ochronosis occurs in ALKAPTONURIA, but has also been associated with exposure to certain chemicals (e.g., PHENOL, trinitrophenol, BENZENE DERIVATIVES).

Homogentisic acid is an organic compound that is an intermediate metabolite in the catabolic pathway of tyrosine and phenylalanine, and its accumulation in the body can lead to a rare genetic disorder known as alkaptonuria.

An enzyme that catalyzes the conversion of 4-hydroxyphenylpyruvate plus oxygen to homogentisic acid and carbon dioxide. EC 1.13.11.27.

Facial dermatoses refers to various skin conditions that affect the face, causing symptoms such as redness, inflammation, papules, pustules, scaling, or pigmentation changes, which can be caused by a range of factors including genetics, infections, allergies, and environmental factors.

Cyclohexane ring substituted by one or more ketones in any position.

Non-heme iron-containing enzymes that incorporate two atoms of OXYGEN into the substrate. They are important in biosynthesis of FLAVONOIDS; GIBBERELLINS; and HYOSCYAMINE; and for degradation of AROMATIC HYDROCARBONS.

Excessive pigmentation of the skin, usually as a result of increased epidermal or dermal melanin pigmentation, hypermelanosis. Hyperpigmentation can be localized or generalized. The condition may arise from exposure to light, chemicals or other substances, or from a primary metabolic imbalance.

Benzoic acid or benzoic acid esters substituted with one or more nitro groups.

General disorders of the sclera or white of the eye. They may include anatomic, embryologic, degenerative, or pigmentation defects.

'Joint diseases' is a broad term that refers to medical conditions causing inflammation, degeneration, or functional impairment in any part of a joint, including the cartilage, bone, ligament, tendon, or bursa, thereby affecting movement and potentially causing pain, stiffness, deformity, or reduced range of motion.

Oxidases that specifically introduce DIOXYGEN-derived oxygen atoms into a variety of organic molecules.

Works containing information articles on subjects in every field of knowledge, usually arranged in alphabetical order, or a similar work limited to a special field or subject. (From The ALA Glossary of Library and Information Science, 1983)

An essential aromatic amino acid that is a precursor of MELANIN; DOPAMINE; noradrenalin (NOREPINEPHRINE), and THYROXINE.

Cartilage of the EAR AURICLE and the EXTERNAL EAR CANAL.

Resorcinols are aromatic organic compounds containing two hydroxyl groups attached to a benzene ring, known for their antiseptic and antibacterial properties, used in various medical and cosmetic applications.

Hydroquinones are chemical compounds that function as potent depigmenting agents, inhibiting the enzymatic conversion of tyrosine to melanin, used topically in the treatment of various dermatological disorders such as melasma, freckles, and hyperpigmentation.