Ascorbic acid transport by 3T6 fibroblasts. Regulation by and purification of human serum complement factor.
It was earlier reported (Padh, H., and Aleo, J. J. (1987) Proc. Soc. Exp. Biol. Med. 185, 153-157) that the activation of serum complement by endotoxin or immunocomplexes inhibited ascorbate transport in 3T6 fibroblasts. We show here that the inhibitor of 3T6 fibroblasts. We show here that the inhibitor of ascorbate transport increased the Km for ascorbate without affecting the Vmax, indicating that the inhibitor reduces the affinity of the ascorbate transporter for ascorbate without affecting the process of translocation. Inhibition by serum and endotoxin was reversible, and the generated inhibitor was no longer heat-labile (at 56 degrees C for 30 min) suggesting that the inhibitor of ascorbate transport is likely to be a small protein molecule. Utilization of complement components suggested that C3 was consumed during formation of the inhibitor of ascorbate transport while C5 and factor B were not consumed. These data along with other results indicate that the inhibitor is generated at C3 step of complement activation. The inhibitor was purified from inulin activated human serum and it had an apparent molecular mass of around 9000 daltons. The inhibitory effect of the purified factor was abolished by antiserum to C3a suggesting that the 9000-dalton factor could be related to this fragment of complement protein. These data raise the possibility that tissue supply of ascorbate may be compromised during infection or autoimmune processes when serum complement is activated.
Padh
H
H
Department of Pathology, Temple University School of Dentistry, Philadelphia, Pennsylvania 19140.
Aleo
J J
JJ
D000818:Animals; D001205:Ascorbic Acid / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D002413:Cations, Divalent / Q000494:pharmacology; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D003167:Complement Activation; D003176:Complement C3 / Q000502:physiology; D015926:Complement C3a; D003165:Complement System Proteins / Q000302:isolation & purification* / Q000502:physiology; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D051379:Mice; D008970:Molecular Weight
D002413:Cations, Divalent; D003176:Complement C3; D015926:Complement C3a; D003165:Complement System Proteins; D001205:Ascorbic Acid