Castles Intrinsic Factor

In the years 1929-37 Castle and his colleagues showed that normal gastric juice (intrinsic factor) would potentiate the hemopoietic effect of beef muscle (extrinsic factor). Later they showed that the extrinsic factor in beef muscle was vitamin B12 (Gardner et al., 1949) and that vitamin B12 itself acted like extrinsic factor when small doses were administered orally (Berk et al., 1948b). 

Meanwhile there were many unsuccessful attempts to isolate the intrinsic factor, which is heat-labile and readily inactivated by chemical procedures (see reviews by Ungley, 1951-52 Welch and Heinle, 1951 Welch and Nichol, 1952 Castle, 1953 E. L. Smith, 1954 SchiUing, 1954). 

At one time intrinsic factor could be assayed only by its capacity to potentiate the hemopoietic effect of small doses of extrinsic factor (vitamin Bi2) in patients with pernicious anemia in relapse (page 157). The ability of materials to bind vitamin B12 and render it unavailable to organisms used for microbiological assay (page 168) proved to be an 

For several years Glass and his colleagues (1952) have held the view that Castle s intrinsic factor was identical with or associated with the soluble glandular mucoprotein fraction of normal gastric juice. This muco-protein was believed to come from the cells at the neck of glands in the fundus (corpus) mucosa of the human stomach. During electrophoresis this substance moved towards the anode, and was the most acid protein in gastric juice. 

Schilling and Deiss (1953) added radioactive Bu to gastric juice prior to electrophoresis on paper. The radioactive B12 was bound to a component of gastric juice which was not one of the major protein peaks and which moved towards the anode. 

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Castle then showed (1929) that beef muscle was as effective as liver in preventing pernicious anemia, provided it was administered with normal gastric juice. He therefore concluded two factors were involved—an extrinsic one which was a component in liver or muscle and an intrinsic factor which was secreted by the stomach. Major efforts were therefore directed at identifying the extrinsic factor in liver or other meats. 

In 1926, Minot and Murphy controlled pernicious anemia using liver. In 1944, Castle demonstrated intrinsic factor needed to control pernicious anemia with liver. Rickes et al., in 1948, isolated and crystallized fiictor in liver controlling pernicious anemia In that same year, Smith and Parker crystallized and designated liver factor as vitamin B12. West demonstrated, m 1948. clinical activity of vitamin B12. and. in 1955, Hodgkin et al. determined the structure of the vitamin. This is shown in Structure 1. Vitamin Blz is the only vitamin with a metal ion—in this case, cobalt. 

Cobalamin binding protein Intrinsic factor of Castle... 

Bi2 (2). Corrinoids are sequestered from food sources by a glycoprotein of mass 45kDa called intrinsic factor, which is secreted in the stomach and binds B12 derivatives very tightly (for CN-Cbl, iC = 1.5 X 10 mol dm ). Several other proteins bind and transport B12 into cells (3). The disease pernicious anemia has been recognized since the early nineteenth century and linked to a deficiency of what William Castle called extrinsic factor (i.e., vitamin B12) in 1928 (1). This disease develops because of the failure of the patient to secrete sufficient intrinsic factor. 

One aspect of the biological activity of the glandular mucoprotein fraction was its relationship to Castle s intrinsic factor (GIO, G37). A daily dose of 50-100 mg of this material, when given to pernicious anemia patients with small oral doses of vitamin Bis, brought about a striking hematopoietic response. This activity was due, as we now know, to the content of the proteolytic degradation product of intrinsic factor (G12, G14, G18, G20, S22). 

The work of the past 35 years has confirmed Castle s initial concept (C5-C10) of a principle in human gastric juice necessary for normal hematopoiesis (G2Q). Its lack in the gastric content of pernicious anemia patients was recognized, as early as 1929 (C5, C9), to be the essential defect leading to the development of pernicious anemia, through failure of the reaction between extrinsic factor, now known to be identical with vitamin B12, and intrinsic factor in normal human gastric juice. Other investigators confirmed that IF is formed by the fundus and body of the stomach in man (see G20) and by the pyloric end of the stomach in the hog (L2, M33), and that it is absent from saliva. 

Osgood demonstrated that pernicious anemia serum delays maturation of megaloblastic bone marrow (see LI). The work of Callender and Lajtha (see G20) points out that addition of normal gastric juice potentiates the effect of vitamin B12 in counteracting this maturation-delaying effect of pernicious anemia serum. A B12 binder separated from normal gastric juice by electrophoresis or ammonium sulfate precipitation was also shown to enhance the B12 effect on maturation of the erythro-blasts, when added to bone marrow (P2, P3). The relation of this maturation-promoting factor to Castle s intrinsic factor is not clearly defined (see G20). 

C6. Castle, W. B., Development of knowledge concerning the gastric intrinsic factor and its relation to pernicious anemia. New Engl. J. Med. 249, 603-614 (1953). 

TIO. Taylor, K. B., An antibody to Castle s intrinsic factor. Haematol. Latina (Milan) 2, 181-186 (1959). 

Castle s intrinsic factor a substance produced by the stomach which combines with the extrinsic factor (vitamin B12) in food to yield an antianemic principle, its lack is believed to cause pernicious anemia cation exchange capacity a measure of the capability of a substance or a (solid) material to bind cations in a reversible marmer CCP see CCPAES... 

Cooper and Castle have proposed a three-step sequence to explain the vitamin B12 absorption in the gastrointestinal tract. In the first step, vitamin B12 binds with the intrinsic factor in gastric juice. The affinity of the vitamin for the intrinsic factor is thought to be greater than its affinity for proteins in the intestinal content consequently, the intrinsic factor (IF) successfully displaces the vitamin from its weaker bonds with other proteins. Calcium facilitates and EDTA inhibits the absorption of vitamin B12 by the everted intestine. On the basis of these and related findings, workers proposed the second step in vitamin Bi2 absorption. At that stage it is assumed that the intrinsic factor-vitamin B12 complex is trapped in the intestinal wall by the intermediate of calcium bonds and absorbed by pinocytosis. This stage of the absorption process probably is interfered with in sprue and steatorrhea where calcicum soaps are formed in the intestinal lumen. 

The story of the intrinsic factor involves as well the whole story of pernicious anemia and of vitamin B12. William Bosworth Castle, the discoverer of the intrinsic factor, has described the history of The Conquest of Pernicious Anemia, but only those parts will be touched on here that are needed to make the story of the intrinsic factor intelligible. 

Ungley CC, Moffett R. Observations on Castle s intrinsic factor in pernicious anaemia. Lancet 1 1232-1235, 1936. 

For review, see Glass (n. 318). The story of the partial isolation of intrinsic factor can be followed in Glass GBJ, Boyd LJ, Rubenstein MH, et al. Relationship of glandular mucoprotein from human gastric juice to Castle s intrinsic antianemic factor. Science... 

Hoedemaker PJ, Abels J, Wachters JJ, et al. Investigations about the site of production of Castle s gastric intrinsic factor. Lab Invest 13 1394-1399, 1964. 

Fisher JM, Taylor KB. The intracellular localization of Castle s intrinsic factor by immunofluorescent technique using autoantibodies. Immunology 16 779-784, 1969. 

The Diagnosis of Deficiencies of Vitanun Bn and Intrinsic Factor in Man 153 Castle s Intrinsic Factor. 154... 

Loss of Castle s intrinsic factor leads to defective absorption of vitamin B12, and so to depletion. 

Castle originally postulated an interaction between an intrinsic (gastric) factor and an extrinsic (food) factor, leading to the production of the liver active principle. He and his colleagues later showed (Berk et al., 1948b) that vitamin Bi2 functioned as extrinsic factor, i.e., its effect when orally administered in small doses to patients with pernicious anemia was potentiated by giving a source of intrinsic factor orally at or about the same time (see page 157). 

The suggestion of Glass et al. (1954) that in addition to Castle s intrinsic factor there may be an intramural intestinal Bu acceptor (analo ... 

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