Immunological properties of human vitamin B12 binders

Finkler, Alexander E.; Green, Pamela D.; Hall, Charles A.

doi:10.1016/0005-2795(70)90053-x

Cited by 42 publications

(8 citation statements)

References 11 publications

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“…(Fig. 1) (13,14), it has been suggested that granulocytes are the source of this serum protein (5). This concept is further supported by the presence of high levels of this protein in the sera of patients with CML (1) and the fact that granulocytes in vitro synthesize a protein with elution properties similar to the leukocyte B,2 binder (5).…”

Section: Gel Filtration Studies Sephadex G-200 Was Obtained Frommentioning

confidence: 99%

Release of vitamin B12—binding protein by human leukocytes in vitro

Corcino¹,

Krauss²,

Waxman³

et al. 1970

J. Clin. Invest.

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A B S T R A C T Human granulocytes (G) contain a vitamin Ba-binding protein (B12BP).There is evidence that chronic myelogenous leukemia leukocytes (CMLL) may synthesize B12BP. Our prior studies suggested that intact, living intravascular G synthesize and release such protein into extracellular compartments in vivo.In the present study, CMLL were incubated in Trisbuffered Hank's basal salt solution (pH 7.2) containing 0.1% human serum albumin to study release of B12BP into the medium. B,2BP was released continuously and in increasing amounts over a 5 hr period at 370C; this release was inhibited almost completely when the cells were incubated at 4VC and by about half as much in the presence of N-ethylmaleimide (1 mmole/liter). Cycloheximide (50 ,gg/ml) had no effect on the release of B12BP but significantly inhibited incorporation of leucine-'H into leukocyte protein. G incubated with 20 mg/ml of compound 48/80, an experimental histamine-releasing agent, had a 6-fold increase in release of B12BP over a 2 hr period. Subcellular fractionation studies of human granulocytes demonstrate that most of the B12BP is associated with the granular (20,000 g) layer with an excellent correlation observed between its subcellular distribution and that of acid phosphatase.These findings suggest that the release of B12BP from G is mediated by an active process and provide further evidence that granulocytes are secretory as well as phagocytic cells.

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Section: Gel Filtration Studies Sephadex G-200 Was Obtained Frommentioning

confidence: 99%

Release of vitamin B12—binding protein by human leukocytes in vitro

Corcino¹,

Krauss²,

Waxman³

et al. 1970

J. Clin. Invest.

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“…After that time and up to 31 days, there was sufficient TC II-B12 to count, but the limits of the TC II peaks were indistinct, making precise quantitation difficult. The TC II recovered from the gel filtrations of samples up to and including that of day 3 was tested by reaction with anti-TC II as described previously (22). Subsequently, the activity of TC II was too low to permit this step.…”

Section: Methodsmentioning

confidence: 99%

Transcobalamins I and II as natural transport proteins of vitamin B12.

Hall¹

1975

J. Clin. Invest.

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A B S T R A C T There are two conflicting theories of how plasma vitamin Ba (Bv2) is transported in man: (a) by two distinct transport proteins, transcobalamins I and II (TC I and II), each having a specific role and time of function; and (b) by three active transport proteins, TC I, II, and III, that take up B12 randomly in proportion to the unsaturated amounts of each. To test these theories a man was given 1.12 ,ug, 229 ACi, of ['7Co] B1 mixed with food. Blood samples were taken several times on the 1st day and at lengthening intervals up to day 51. The amount of TC II-B12 was measured in each sample by: gel filtration and by precipitation with (NH4)aSOi. Total serum R-Bi was then separated into TC I and TC III by: (a) a single step anion exchange system and (b) isoelectric focusing (IEF). As the B21 was being absorbed, 92-95% of that in venous blood was carried by TC II. Absolute and percentage transport by TC II declined sharply during the first 24 h; between days 7 and 51 20-33% of the label was on TC II, and the rest was carried by R-type binders. Absolute transport by TC I did not reach a maximum until after day 1 and before day 3. Transport by an as R-type binder, TC III, could not be demonstrated. TC I was isoelectrically heterogenous, with the components focusing between pH 2.9 and 3.35. It was concluded that (a) TC II is the dominant carrier of B,2 immediately after absorption; (b) maximum transport by TC I requires the passage of time after absorption; (c) after the absorbed Bn reaches equilibrium with the total body Bu. about one fourth of the plasma B22 is carried by TC II and three fourth by TC I; and (d) TC I and TC II are the only functional transport proteins of plasma B,2.

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“…Total folate binding was estimated after removal of endogenous folate by acid exposure and dextran coated charcoal separation. 9 The labelled cobalamin binding proteins were chromatographed on Sephadex G-200 using 40 mmolI phosphate buffer, pH 7.4, containing 0 5 mol/l sodium chloride, to enable the type of binding protein present to be established. "…”

Section: Tissue Studiesmentioning

confidence: 99%