Feb 13, 1989

Hydrophobic erythrocyte folate binding proteins are converted to hydrophilic forms by trypsin in vitro

Biochimica Et Biophysica Acta
A C Antony, R S Verma

Abstract

Human erythrocyte membranes contain high-affinity folate-binding proteins (FBPs) which on solubilization with detergents resolve into apparent 160,000 Mr moieties on Sephacryl S-200 gel filtration in Triton X-100. These FBPs share antigenic and ligand binding characteristics with particulate FBPs from other human tissues. During studies to define the vectorial orientation of these FBPs on the erythrocytes, we trypsinized intact cells with 250 micrograms trypsin per ml packed cells and quantitatively analysed the remaining cell-associated FBPs as well as the products of proteolysed FBPs in the supernatant. Incubation of intact cells with trypsin resulted in a dose-dependent decrease in their capacity to bind 125I-labelled pteroylglutamate (histamine derivative); at 250 micrograms/ml trypsin, folate binding was decreased by 77% compared to nontrypsin-treated control cells. While trypsinized cells contained proportionately lower quantities of apparent 160,000 Mr FBPs than untreated control cells, the supernatant of trypsinized cells (soluble phase) contained a single species of Mr = 40,000 which retained folate binding capacity. The sum of FBPs in trypsin supernatant and trypsin-treated cells was 87% of that found in untreated cel...Continue Reading

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Mentioned in this Paper

Centrifugation, Density Gradient
Hormone Receptors, Cell Surface
Red Cell Ghost
Molecular Sieve Chromatography
Carrier Proteins
Folic Acid, Sodium Salt
Trypure
Folate Receptors, GPI-Anchored

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