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Isolation of Alternative Pathway C3 Convertase Containing Uncleaved B and Formed in the Presence of C3 Nephritic Factor (C3NeF)

From the Departments of Medicine, Harvard Medical School and the Robert B. Brigham Hospital, Boston, Massachusetts 02120

Abstract

The capacity of serum from patients with membranoproliferative glomerulonephritis to interact with normal human serum to inactivate C3 was ascribed to the presence of C3 nephritic factor³ (C3NeF)⁴ (1). The action of C3NeF was magnesium ion dependent, operative in C4 deficient serum (2), and impaired in serum selectively deficient in B and (3) indicating that C3 cleavage occurred by the alternative pathway. Fluid phase interaction of C3, B, and in the presence of C3NeF permits recovery of C3 convertase with an estimated sedimentation rate of 10S containing at least C and (4). The present study shows that interaction of larger amounts of C3NeF with C3 and B in the absence of allows isolation of a 10S complex containing C3 and , an uncleaved form of B, and manifesting C3-cleaving activity.

Materials and Methods. B (5), (6, 7), (7), and C3 (8, 9) were purified to homogeneity and quantitated as described.

Footnotes

³ Nomenclature: In the provisional nomenclature for the alternative pathway factors: B is synonymous with C3 proactivator and glycine-rich glycorprotein (GBG); with C3 proactivator convertase; P represents properdin. A bar over a letter indicates the activated form of a protein.

⁴ Abbreviations used in this paper: C3NeF, C3 nephritic factor; GVB, Veronal-buffered saline with magnesium, calcium, and gelatin; DGVB, GVB with dextrose;^*, labeled.

¹ Postdoctoral fellow of the Dutch Kidney Foundation.

² Postdoctoral fellow of the Helen Hay Whitney Foundation.

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