hæm, heme
(hiːm)
[Back-formation from hæmoglobin.]
a. A chelation compound, C34H32O4N4Fe, of ferrous ion and protoporphyrin, obtained on reduction of hæmatin: the red-coloured non-protein constituent of hæmoglobin.
| 1925 Anson & Mirsky in Jrnl. Physiol. LX. 50 Haemoglobin is a conjugated protein consisting of globin and a non-protein part, containing pyrrol nuclei and iron, which we shall call haem. 1939 Jrnl. Biol. Chem. CXXXI. 661 Coryell..has applied the Pauling equation..to the oxidation of hemoglobin..and has shown that interaction among the four heme groups will account for the occurrence of an n which is not integral. 1956 Nature 11 Feb. 275/1 The angular variation of the g values enables an accurate determination to be made of the orientation of the hæm and porphyrin planes with respect to the external crystalline axes. Ibid. 275/2 Detailed information on the orientation of the hæm planes can be combined with X-ray measurements to calculate the polypeptide chain directions. 1970 R. W. M{supc}Gilvery Biochem. ii. 13 The biological function of hemoglobin is therefore derived from both the heme and the peptides... Each of the four peptide chains has its own heme. |
b. Any of various compounds of a ferrous or ferric ion and a porphyrin, present in biological pigments.
| 1948 Biochem. Jrnl. XLII. p. xlvii/2 The phase separation of haems has been applied to ox heart muscle. 1962 Rimington & Kennedy in Florkin & Mason Comprehensive Biochem. IV. xii. 563 By far the most important metalloporphyrins..are the iron complexes or hemes. In these nature has exploited the valency change from the ferric to ferrous state and vice versa to establish an electron transport system connecting the intracellular dehydrogenases with atmospheric oxygen. 1966 K. Okunuki in Florkin & Stotz Comprehensive Biochem. XIV. 233 Four types of haem have so far been known to occur in cytochromes... These are haem a, protohaem, haem c and so-called haem a2. |