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Biochemical data indicate mu-opioid receptor (MOR) coupling predominantly to the G(i) and G(o) family. Additionally, MOR coupling to G(s) is suggested by pharmacological assessments that have revealed excitatory MOR effects, which are resistant to pertussis toxin and sensitive to cholera toxin. However, biochemical evidence for such interactions remains(More)
Transcobalamin II (TCII) is a plasma protein essential for the transport and cellular uptake of vitamin B12 (B12; cobalamin, Cbl). Congenital deficiency of functional TCII is an autosomal recessive genetic disorder that results in clinical B12 deficiency usually within several months following birth. In this report, we describe the molecular basis for TCII(More)
The KB cell, a transformed human cell line, constitutively expresses a high level of the glycosylphosphatidylinositol (GPI) anchored folate receptor protein alpha (FR alpha) and thereby can grow in medium containing <1 nM folate. When transferred from a folate-replete (FR) medium to one folate-deficient (FD), intracellular folate diminishes about 50-fold(More)
This study was designed to identify the cellular component of the intestinal villus where transcobalamin II (TCII) is synthesized, because this protein provides an essential function in the intestinal absorption of vitamin B(12) (cobalamin, Cbl). When a segment of proximal or distal small intestine of the guinea pig is cultured in medium containing(More)
Transcobalamin II (TCII) is a plasma protein that binds vitamin B12 (cobalamin; Cbl) and facilitates the cellular uptake of the vitamin by receptor-mediated endocytosis. In genetic disorders that are characterized by congenital deficiency of TCII, intracellular Cbl deficiency occurs, resulting in an early onset of megaloblastic anemia that is sometimes(More)
The cellular uptake of cobalamin (Cbl, vitamin B12) is mediated by transcobalamin II (TCII), a plasma protein that binds Cbl and is secreted by human umbilical vein endothelial (HUVE) cells. These cells synthesize and secrete TCII and, therefore, served as the source of the complementary DNA (cDNA) library from which the TCII cDNA was isolated. This(More)
Chronic morphine augments protein kinase C (PKC) phosphorylation of G(beta), which enhances the potency of G(betagamma) to stimulate adenylyl cyclase II (ACII) activity. The present study demonstrates an in vivo association between phosphorylated G(beta) and a specific PKC isoform, PKCgamma. We investigated the association of G(beta) and PKCgamma by(More)
A folate-binding protein (FBP) anchored to cell membranes by a glycosyl phosphatidylinositol (GPI) adduct is constitutively expressed in some transformed and cultured cell lines. Its expression is upregulated when these cells are grown in medium containing low folate, but whether this occurs in vivo with nutritional folate deficiency is unknown. To address(More)
A complementary DNA (cDNA) clone coding for transcobalamin II (TCII) has been isolated from a human umbilical vein endothelial cell cDNA library. The cDNA is 1.9 Kb and includes the nucleotide sequence which encodes the NH2-terminal 19 amino acids of human TCII. The size of the cDNA is sufficient to code for the entire protein and also contains the(More)
Transcobalamin II (TCII) is a plasma protein that transports cobalamin to tissues for cellular uptake by receptor-mediated endocytosis. Human umbilical vein endothelial cells (HUVEC) in culture constitutively express TCII. However, in other cell lines, TCII expression is dependent on high cell density. ECV304, a cell line with some properties of HUVEC,(More)