Shimomura O
Symp Soc Exp Biol. 1985;39:351-72.
Photoproteins are the primary reactants of the light-emitting reactions of various bioluminescent organisms. A photoprotein emits light in proportion to its amount, like a luciferin, but its light-emitting reaction does not require a luciferase. There are about two dozen types of bioluminescent organisms for which substantial biochemical knowledge is presently available, and about one third of them involve photoproteins. Most photoproteins are found in marine organisms. There are various types of photoproteins: the photoproteins of coelenterates, ctenophores and radiolarians require Ca2+ to trigger their luminescence; the photoproteins of the bivalve Pholas and of the scale worm appear to involve superoxide radicals and O2 in their light-emitting reactions; the photoprotein of euphausiid shrimps emits light only in the presence of a special fluorescent compound; the photoprotein of the millipede Luminodesmus, the only known example of terrestrial origin, requires ATP and Mg2+ to emit light. The Ca2+-sensitive photoproteins of coelenterates have been most frequently studied and most widely used. Therefore, they are overwhelmingly popular compared with other types. All coelenterate photoproteins, including aequorin, halistaurin, obelin and phialidin, have relative molecular masses close to 20 000, contain an identical functional group, and emit blue light in aqueous solution when a trace of Ca2+ is added, in the presence or absence of molecular oxygen. Aequorin contains an oxygenated form of coelenterazine in its functional group. When Ca2+ is added, aequorin decomposes into three parts, i.e., apo-aequorin, coelenteramide and CO2, accompanied by the emission of light. Apo-aequorin can be reconstituted into active aequorin indistinguishable from the original sample, by incubation with an excess of coelenterazine in a buffer containing 5 mM-EDTA and a trace of 2-mercaptoethanol, even at 0 degree C. Thus, aequorin and other coelenterate photoproteins can be luminesced and recharged repeatedly. The regeneration of coelenterate photoproteins in this manner probably takes place in vivo, utilizing stored coelenterazine. The photoproteins of coelenterates, and their chemically modified forms, are useful in measuring and monitoring calcium ions in biological systems, especially in single cells.
光蛋白是各种生物发光生物体发光反应的主要反应物。光蛋白像荧光素一样，其发光量与其含量成正比，但其发光反应不需要荧光素酶。目前有大约二十多种生物发光生物体，我们对它们有大量的生化知识，其中约三分之一涉及光蛋白。大多数光蛋白存在于海洋生物中。光蛋白有多种类型：腔肠动物、栉水母和放射虫的光蛋白需要Ca2+来触发其发光；双壳贝类笋螺和多鳞虫的光蛋白在其发光反应中似乎涉及超氧自由基和O2；磷虾的光蛋白仅在一种特殊的荧光化合物存在时才发光；千足虫Luminodesmus的光蛋白是唯一已知的陆地来源的例子，它需要ATP和Mg2+来发光。腔肠动物对Ca2+敏感的光蛋白研究得最频繁，使用得也最广泛。因此，与其他类型相比，它们极其受欢迎。所有腔肠动物光蛋白，包括水母发光蛋白、海月水母发光蛋白、绿荧光蛋白和海鳃发光蛋白，相对分子质量接近20000，含有相同的官能团，并且在添加微量Ca2+时，无论有无分子氧，在水溶液中都会发出蓝光。水母发光蛋白在其官能团中含有腔肠素的氧化形式。当添加Ca2+时，水母发光蛋白分解成三个部分，即脱辅基水母发光蛋白、腔肠酰胺和CO2，同时发光。脱辅基水母发光蛋白可以通过在含有5 mM - EDTA和微量2 - 巯基乙醇的缓冲液中与过量的腔肠素孵育，即使在0摄氏度下，也能重新组装成与原始样品无法区分的活性水母发光蛋白。因此，水母发光蛋白和其他腔肠动物光蛋白可以反复发光和充电。腔肠动物光蛋白以这种方式的再生可能在体内利用储存的腔肠素发生。腔肠动物的光蛋白及其化学修饰形式可用于测量和监测生物系统中的钙离子，尤其是在单细胞中。
