Species Specificity in the Immunologic Reactions and Biological Functions of Transcobalamin II

Haus, Mary; Green, Pamela D.; Hall, Charles A.

doi:10.3181/00379727-162-40668

Cited by 7 publications

(2 citation statements)

References 6 publications

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“…The HepG2 hepatocytes, derived from a human hepatoma, were found to have receptors for TC II-Cbl, internalized the complex, released the Cbl from the TC 11, converted it to coenzyme forms of Cbl, and released Cbl into the environment. The conditions and dynamics of the binding of TC II-Cbl by HepG2 cells were similar to those of other human cells.Those studied in the greatest detail include HeLa cells (Finkler and Hall, 1967;Haus et al, 1979;Hall and Green , 1978;Hall et al, 1979), fibroblasts (Youngdahl-Turner et al, 1978), an established line of lymphoblasts (Hall and Green, 1978), and stimulated peripheral lymphocytes (Hall 1984). The binding to HepG2 cells was saturable, Ca2' dependent, and inhibited by a large excess of TC II-Cbl (Fig.…”

Section: Discussionmentioning

confidence: 99%

“…The HepG2 cell was also known to contain receptors for standard asialoglycoproteins (Schwartz et al, 1981(Schwartz et al, , 1982. It was essential that cell and binder come from the same species because the transport system is known to exhibit species specificity for TC 11 (Haus et al, 1979). It may also be significant that the human hepatocyte is naturally exposed to R binder.…”

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The metabolism of cobalamin bound to transcobalamin II and to glycoproteins that bind Cbl in HepG2 cells (human hepatoma)

Hall

Green-Colligan

Begley

1985

Journal Cellular Physiology

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The binding, internalization, processing and release of labeled cyanocobalamin (CN[57Co]Cbl) bound to human transcobalamin II (TC II) were studied in HepG2 cells, a line of hepatocytes derived from a human hepatoma. The cells bound the TC II-Cbl by specific, high affinity receptors. Within the cell, the CN-Cbl was promptly freed from TC II and the CN-Cbl converted to more active forms including adenosyl Cbl (AdoCbl) and methyl Cbl (MeCbl). Whereas free labeled Cbl was still present at 72 hours after entry, the cells also bound Cbl to an intracellular binder (ICB) presumed to represent the holo enzymes dependent on Cbl. At levels of TC II that saturated the receptors for TC II-Cbl, much of the Cbl entering the cells remained free and was converted to AdoCbl. Under these circumstances the cells released free Cbl, mostly AdoCbl. Human R type binders of Cbl, which are glycoproteins and some having a terminal galactose, were bound by the HepG2 cells. The binding was characteristic of the receptor system responsive to a terminal galactose, or asialoglycoproteins, but was inconsistent and of low affinity. Cbl bound to R binder was internalized and converted to coenzyme forms of Cbl, but the process was much less effective than when the Cbl entered via the TC II receptor system. It was concluded that the receptors for R-Cbl were unlikely to contribute to the physiologic transport of Cbl in man, but may function in some yet unknown way.

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Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

The metabolism of cobalamin bound to transcobalamin II and to glycoproteins that bind Cbl in HepG2 cells (human hepatoma)

Hall

Green-Colligan

Begley

1985

Journal Cellular Physiology

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The Proteins of Transport of the Cobalamins

Hall¹

1989

Folates and Cobalamins

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Genetic patterns of transcobalamin II and the relationships with congenital defects

Fràter‐Schröder

1983

Mol Cell Biochem

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The vitamin B12-binding protein, transcobalamin II, is a trace component of plasma with a rapid turnover. This protein is essential for absorption, transport, cellular uptake and for recycling of vitamin B12 (cobalamin). Congenital transcobalamin II deficiency, an inborn error of metabolism is inherited as a recessive trait. The homozygous form of the deficiency is accompanied by severe clinical, hematological and immunological disturbances in the first months of life. Analytical, genetic, biochemical and clinical aspects of transcobalamin II in man and in vertebrates have been reviewed here. A genetic polymorphism for the protein has been found in man, rabbits and mice. Family studies revealed that the genetic patterns in man are determined by four polymorphic and several rare alleles. This genetic variability has been applied in paternity testing and in population studies. Transcobalamin II typing in families of patients with the inherited functional deficiency has led to identification of various deficient alleles in heterozygous carriers of the defects. Applying transcobalamin II typing after bone marrow transplantation demonstrated that this protein originates partly in the bone marrow. Subsequent investigations in cell culture have shown that human skin fibroblasts and cultured bone marrow synthesize and secret isotypes of a transport protein corresponding to the genetic isotypes observed in plasma. Comparison of transcobalamin II types in umbilical cord serum with the maternal types, has proven that the transcobalamin II activity in the cord serum is derived from the fetus. This finding will be of crucial importance in the early diagnosis of the deficiency syndrome.

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Species Specificity in the Immunologic Reactions and Biological Functions of Transcobalamin II

Cited by 7 publications

References 6 publications

The metabolism of cobalamin bound to transcobalamin II and to glycoproteins that bind Cbl in HepG2 cells (human hepatoma)

The metabolism of cobalamin bound to transcobalamin II and to glycoproteins that bind Cbl in HepG2 cells (human hepatoma)

The Proteins of Transport of the Cobalamins

Genetic patterns of transcobalamin II and the relationships with congenital defects

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