PIGMENTS

PIGMENTS, various organic compounds that provide color to animal and plant tissues. Pigments are extremely widespread in animals and plants and determine the diversity of their colors. The greatest biological significance belongs to the group of water-soluble pyrrole derivatives I, /NH, to which respiratory pigments belong: hemoglobin of animals and chlorophyll of plants; bile pigments (see Gall) and porphyrins (see) also belong to this group. The group of carotenoids (see) is very widespread, representing unsaturated hydrocarbons or their oxygen derivatives. Yellow plant pigments, which have importance in the dyeing industry, are for the most part flavone derivatives | | Pen - Very widespread are pigments that determine the blue, red, and purple coloration of most flowers and some fruits, namely anthocyanin glycosides, which are very close to flavone derivatives. Derivatives of anthraquinone (see) are certain pigments that have therapeutic importance (aloin, chrysarobin, chrysophanic acid, emodin) and histological technique value (carmine). Among the pigments there are also protein substances (proteids): hemoglobin, oxyhemocyanin (blue, copper-containing pigment of the blood of some lower animals), phycocyanin and phycoerythrin of algae. The structure of many pigments has not been clarified or has been insufficiently clarified; in addition to colored proteids, these include: hematoxylin (see), blue cyanocrystallin of the carapace of crustaceans, which turns red crus-taceorubin under the action of acids or when boiled with water, tetronerithrin, found around the eyes of grouse, violet-red turacin of the feathers of some birds, visual purple, melanins, most pigments of normal and pathological urine, pyocyanin, and various pigments produced by microbes, and numerous pigments of plants and lower animals.

V. Gulevich. Pigments of bacteria, coloring substances that color a bacterial culture in a specific color or in some species only certain strains; pigments produced by bacteria in most species pass into the environment, more or less intensely coloring it. Conditions that promote the production of pigments are O₂ of the air, a certain temperature, a certain composition of the nutrient substrate. Under anaerobic conditions, pigments are usually not formed; for saprophytes 20-25°C and for pathogenic forms 37°C are the temperatures most favorable for their production; the medium on which pigments form most easily and abundantly is potato; for the formation of some of them special conditions are necessary; thus, for the formation of the red pigment prodigiosin, the presence of magnesium, iron, and zinc is necessary. In the vast majority of pigmented bacteria, pigments do not play a role in nutrition and represent a metabolic product diffusing from bacterial cells into the surrounding fluid or being excreted from them in the form of insoluble particles; in some bacteria (green, purple) pigments perform a certain function in the nutrition of microbes. Fluorescent pigments may play a protective role, as they have a poisonous effect on protozoa (Noack). Bacterial pigments are classified by solubility in water, alcohol, and other substances. Among the water-soluble pigments are the green-yellow bacteriofluorescin, insoluble in other solvents, blue pyocyanin, and also blue syncyanin. Not soluble in water but soluble in alcohol are the red prodigiosin, which is also soluble in ether and chloroform, and the yellow-red carotin. Not soluble in water or alcohol is the brown pigment found in the nitrogen-fixing species Azotobacter chroococcum. In purple bacteria there is bacteriopurpurin, consisting of red bacterioerythrin and green bacteriochlorophyll. Among the bacteria that produce pigments, we should name the rod of blue pus (Bac. pyocyaneus, producing pyocyanin), the rod of blue milk (Bac. syncyaneus, syncyanin), Bac. prodigiosus (prodigiosin), Staph. pyogenes aureus (carotin), Sarcina lutea (carotin), gonococcus (carotin), purple sulfur bacteria (bacteriopurpurin), etc. (see Bacteria-pigment-forming bacteria, Bacteriopurpurin). Among the bacteria in which only certain strains produce pigment, we should name acid-fast bacilli, including the tubercle bacillus.