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PMID: 830665 Published · ppublish English Journal Article Research Support, U.S. Gov't, P.H.S.

A saturable high affinity binding site for transcobalamin II-vitamin B12 complexes in human placental membrane preparations.

The Journal of clinical investigation ·Vol. 59 ·No. 1 ·1977-01-00 ·Pages 51-8

Friedman PA, Shia MA, Wallace JK

Abstract

Studies were designed to evaluate the binding of binding of vitamin B12 to cell membrane preparations from human placenta. The transcobalamin II-vitamin B12 complex (TCII-B12), which has a much greater affinity for the membranes than vitamin B12 alone, binds to a single saturable binding site with an approximate Ka = 7.2 mM-1. The binding requires a divalent cation and is temperature-dependent. Free TCII can compete with TCII-B12 for the binding site but has somewhat less affinity than does TCII-B12. Rat TCII-B12 has an affinity constant that is less than one-fifth that of human TCII-B12; human TCI-B12, bovine TCII-B12, hog intrinsic factor-B12 (IF-B12), and human IF-B12 do not bind to the membranes. Pretreating the membranes with trypsin causes a marked decrease in subsequent binding; this suggests the binding site includes a relatively exposed membrane protein. These data suggest that a specific cell surface receptor for the TCII-B12 complex exists in placenta. This TCII-B12 receptor can be solubilized with Triton X-100.

MeSH Terms
Binding Sites Blood Proteins/metabolism Cell Membrane/metabolism Female Humans Placenta/cytology Pregnancy Receptors, Drug Transcobalamins/metabolism Vitamin B 12/metabolism
Chemicals
Blood Proteins Receptors, Drug Transcobalamins Vitamin B 12
Authors & Affiliations
3 authors, click to expand affiliations / ORCID
Friedman P A
Shia M A
Wallace J K
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27 references, click to expand
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Article Info
Journal
The Journal of clinical investigation
Abbr.
J Clin Invest
ISSN
0021-9738
DOI
10.1172/JCI108621
Published
1977-01-00
Pages
51-8
Language
English
Region
United States
NLM ID
7802877
PMCID
PMC333331
Subset
IM
External Links
PubMed source DOI: 10.1172/JCI108621 PMC Full Text View journal details
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