pigment
(redirected from Paint pigment)Also found in: Dictionary, Thesaurus, Medical.
pigment
Pigment
(in biology), a coloring substance that is incorporated into body tissues. Pigments are colored by intramolecular chromophores, atomic groups that selectively absorb light in the visible part of the solar spectrum. Pigments play an important and varied role in the life processes of organisms, especially photobiologic processes.
Occurrence. The most widespread pigments, porphyrins and carotenoids, are found in the majority of plants and animals. Porphyrins are included in the chlorophyll molecules of green plants, in bacteriochlorophylls of photosynthesizing bacteria, and in the respiratory pigments of animals, for example, hemoglobin, myoglobin, and chlorocruorin. Cytochromes, which, like hemoglobin, contain the iron-porphyrin complex heme, are very common. Carotenoids, which are unsaturated isoprenoid hydrocarbons, and their oxidized derivatives xanthophylls are yellow, orange, or red pigments and are present in green plants, algae, fungi, and bacteria. Blue-green and red algae contain auxiliary photosynthetic pigments, called phycobilins, whose nonprotein portion consists of a chain of four pyrrole rings; the blue phycobilin is phycocyanin, and the red—phycoerythrin. Structurally similar to the phycobilins is phytochrome, which is found in plants, and the animal-bile pigments, which are formed during the decomposition of hemoglobin. The large group of plant pigments called flavonoids encompasses substances that differ in chemical structure, color, and occurrence, for example, an-thocyanins and flavones. Flavonoids give color to flowers, fruits, and leaves.
The eyes of animals contain visual pigment, which is structurally complex. Other common pigments of plant and animal tissues are the respiratory chromogens, which are derivatives of quinone, and the melanins, which are found in the skin, fur, and hairs of animals. Fungal and bacterial pigments display a wide variety of chemical structures. Pigments that are identical or close in chemical structure may be found in groups of organisms that are phylogenetically distant from each other.
Pigments are usually contained in various cell structures and, less commonly, dissolved in body fluids. For example, chlorophyll is concentrated in chloroplasts, carotenoids in chromo-plasts and chloroplasts, hemoglobin in red blood cells, and flavonoids in the cell sap of plants. Pigments in combination with proteins and lipids are a structural part of biological membranes. Many animal and plant species have specialized pigment cells, or chromatophores.
Biological role. The pigment system links metabolic processes to light from the environment. One of the most important functions of pigments in plants is participation in photosynthesis. The absorption of light by pigments also plays a role in the growth, development, and movement of plants. The most important function of pigments in animals is participation in visual processes. Hemoglobin and other pigments in the blood transport oxygen from the respiratory organs to the tissues. Cytochromes, respiratory chromogens, and certain other pigments act as enzymes in tissue respiration. Carotenoids and flavonoids in plants and melanins in animals protect the organism against the harmful effects of the sun’s ultraviolet light. Pigments account for coloration, an important feature of an organism’s adaptation to the environment. Coloration in plants serves to attract insect pollinators and birds who spread seeds; in animals it helps to protect against enemies and acts as camouflage while the animal stalks prey.
Until the second half of the 19th century, plant and animal pigments, such as alizarin, indigo, and carmine, were widely used as dyes. Some pigments are used in the food-processing industry and medicine, for example, riboflavin, carotene, and antibiotic pigments.
A. A. KRASNOVSKII
In man. Disruption of any stage of pigment metabolism in man results in the accumulation of various metabolic products and in the development of certain diseases. A distinction is made between hereditary and acquired disturbances; the former are caused by hereditary defects in pigment synthesis and in the synthesis of the chemical precursors of pigments in the liver— red blood cells. Acquired disturbances in pigment metabolism can follow prolonged feverish periods, deficiencies of the vitamins folic and pantothenic acids, and liver diseases, including hepatitis, hepatic tumors, and obstructions of the biliary tract. They can also result from poisoning, Addison’s disease, or some blood diseases. Diseases of pigment metabolism occur at all ages with varying frequencies. The hereditary forms are generally seen in children. Three main groups of disturbances of pigment metabolism are recognized: hemoglobinopathies, hyperbilirubinemias, and porphyrias.
IU. A. KNIAZEV
REFERENCES
Tsvet, M. S. Khromofilly v rastitel’nom i zhivotnom mire. Warsaw, 1910.Timiriazev, K. A. Solntse, zhizn’ i khlorofill (vol. 1 of Izbr. soch.). Moscow, 1948.
Prosser, L., and F. Brown. Sravnitel’naia fiziologiia zhivotnykh. Moscow, 1967. Chapters 8 and 19. (Translated from English.)
Biokhimiia rastenii. Moscow, 1968. Chapters 24, 26, and 28. (Translated from English.)
Konev, S. V., and I. D. Volotovskii. Vvedenie v molekuliarnuiu fotobiologiiu. Minsk, 1971.
Lemberg, R., and J. W. Legge. Hematin Compounds and Bile Pigments. New York-London, 1949.
Chemistry and Biochemistry of Plant Pigments. London-New York, 1965.
Photobiology of Microorganisms. London, 1970.
pigment
[′pig·mənt]Pigment
A finely divided material which contributes to optical and other properties of paint, finishes, and coatings. Pigments are insoluble in the coating material, whereas dyes dissolve in and color the coating. Pigments are mechanically mixed with the coating and are deposited when the coating dries. Their physical properties generally are not changed by incorporation in and deposition from the vehicle. Pigments may be classified according to composition (inorganic or organic) or by source (natural or synthetic). However, the most useful classification is by color (white, transparent, or colored) and by function. Special pigments include anticorrosive, metallic, and luminous pigments.