Lipochromes

LIPOCHROMES, nitrogen-free pigments, widely distributed in plants and animals under various names, e.g., zoonerythrin, tetronerythrin, chlorophane, xanthophane, rhodophane, etc. Luteins and carotenoids (see) belong to lipochromes. Lipochromes are soluble in alcohol, ether, CHCl₃, benzene, CS₂, petroleum ether, and acetone. Their extraction is based on the extraction of lipochromes with chloroform and others. In solid form, they are greenish-yellow, yellow, orange, or red; in solutions, they are yellow. Lipochromes are very sensitive to light: they are easily bleached even in diffused daylight. Lipochromes are not saponified by an alcoholic solution of alkalis. Concentrated H₂SO₄ or strong HNO₃ cause a blue, blue-green, or violet coloration in lipochromes. In mammals, yellow lipochromes are found in adipose tissue, blood serum, serous fluids, milk fat, and in corpora lutea (lutein). Lutein (xanthophyll) C₄₀H₅₆O₂ is close to plant xanthophyll, crystallizes in prisms, whetstones, or thin plates with a metallic luster; solutions are golden-yellow; it gives two absorption bands in the blue part of the spectrum. Luteins in the animal organism are found dissolved in cellular fats and impart a yellow color to adipose tissue. Histochemically, luteins cannot be determined in tissues; it is possible to determine them only in cases of a significant reduction in the amount of fatty substance or after preliminary extraction of the luteins. Luteins are more easily determined in pathological cases. The relationships between luteins and the fatty substances in which they are dissolved are still not clear. It is possible that luteins form chemical compounds with lipoids. A parallelism is observed in the content of lutein and cholesterol in tissues: hypercholesterolemia is always accompanied by an increase in the amount of lutein; tissues rich in cholesterol are always colored yellow and contain particularly large amounts of luteins (atrophic adipose tissue of cachectic patients, atherosclerotic plaques, xanthelasmas, xanthomas, carcinoids, etc.). In diabetes, which is known to be accompanied by hypercholesterolemia, a true lipochromatosis develops: together with cholesterol, luteins accumulate in the endothelium of capillaries, primarily in the liver and brain; the color of the skin, especially of the palms and soles, acquires a distinctly yellow hue, and even the bones of the skull are colored yellow-brown.