血红素或血基质（英语：heme）是一种含铁的辅因子，铁原子位于被称为紫质（porphyrin）的大杂环化合物中心。并非所有的紫质分子中都含有铁，但含有紫质的金属蛋白都以血红素为辅因子，这些蛋白质即血红蛋白。血红素能够帮助酶催化其底物分子。 Heme为血基质，而Hemoglobin为血红蛋白，请注意其中的分别。

医学导航：营养学

辅助、代谢、微量元素

病理、失调、症状／人名、先天

药物（A8/11/12）

Heme or haem (from the Greek "Αίμα" which means blood) is a cofactor consisting of an Fe (ferrous) ion contained in the centre of a large heterocyclic organic ring called a porphyrin, made up of four pyrrolic groups joined together by methine bridges. Not all porphyrins contain iron, but a substantial fraction of porphyrin-containing metalloproteins have heme as their prosthetic group; these are known as hemoproteins. Hemes are most commonly recognized as components of hemoglobin, the red pigment in blood, but are also found in a number of other biologically important hemoproteins such as myoglobin, cytochrome, catalase, heme peroxidase, and endothelial nitric oxide synthase.