Document Detail

The interrelationship of the soluble and membrane-associated folate-binding proteins in human KB cells.
MedLine Citation:
PMID:  3536908     Owner:  NLM     Status:  MEDLINE    
Human KB cells produce two immunologically cross-reactive folate-binding proteins: a particulate cell-associated protein which is solubilized by Triton X-100, and a soluble protein which is released into their growth medium. This compartmentation of these two folate-binding proteins provides a convenient system for studies of their biochemical relationship. The two folate-binding proteins behave similarly to the purified particulate and soluble folate-binding proteins of human milk in analysis by radioactive folate binding, Sephacryl S-200 gel filtration profiles, polyacrylamide gel electrophoresis in either Triton X-100 or sodium dodecyl sulfate, and in Triton X-100 binding based on sucrose density gradient ultracentrifugation in H2O and D2O. The two folate-binding proteins were endogenously labeled by pulsing methionine-starved KB cells with [35S]methionine, and each protein was purified to apparent homogeneity by affinity chromatography at different times during the chase with nonradioactive methionine. The time course of the changes in specific activity (moles of [35S]methionine per mole of folate-binding protein) revealed a more rapid initial rate of synthesis and an earlier maximum in specific activity for the cell-associated folate-binding protein than for the soluble folate-binding protein released into the growth medium. Differences in the levels and specific activities of the two folate-binding proteins of cells exposed to cycloheximide compared with simultaneous controls after pulsing with [35S]methionine suggest that, whereas the cell-associated folate-binding protein is probably produced by de novo protein synthesis, the soluble folate-binding protein seems to be produced from a cellular pool of an already synthesized protein. These results combined with the immunologic cross-reactivity of the two folate-binding proteins strongly suggest a precursor-product relationship between them.
M A Kane; P C Elwood; R M Portillo; A C Antony; J F Kolhouse
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Publication Detail:
Type:  Comparative Study; Journal Article; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  The Journal of biological chemistry     Volume:  261     ISSN:  0021-9258     ISO Abbreviation:  J. Biol. Chem.     Publication Date:  1986 Nov 
Date Detail:
Created Date:  1986-12-24     Completed Date:  1986-12-24     Revised Date:  2007-11-14    
Medline Journal Info:
Nlm Unique ID:  2985121R     Medline TA:  J Biol Chem     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  15625-31     Citation Subset:  IM    
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MeSH Terms
Carrier Proteins / isolation & purification,  metabolism*
Cell Membrane / metabolism*
Centrifugation, Density Gradient
Chromatography, Gel
Cycloheximide / pharmacology
Cytosol / metabolism*
Electrophoresis, Polyacrylamide Gel
Immunosorbent Techniques
KB Cells
Methionine / metabolism
Milk, Human / analysis
Polyethylene Glycols / metabolism
Receptors, Cell Surface*
Sulfur Radioisotopes
Grant Support
Reg. No./Substance:
0/Carrier Proteins; 0/Polyethylene Glycols; 0/Receptors, Cell Surface; 0/Sulfur Radioisotopes; 0/folate-binding protein; 63-68-3/Methionine; 66-81-9/Cycloheximide; 9002-93-1/Octoxynol

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