Department of Biochemistry, Glaxo Group Research Ltd., Middx., U.K.
Rat factor D has been purified to homogeneity (10,559-fold) from serum by chromatography on CM-Sepharose Fast Flow, phenyl-Sepharose CL-4B and Mono S and has been shown to resemble its human and mouse counterparts both in substrate specificity and in its susceptibility to inhibition by the organophosphorous inhibitor di-isopropylfluorophosphate. The rat enzyme, however, is heavily glycosylated and binds to wheat-germ lectin-Sepharose 6MB and 5-hydroxytryptamine-agarose, but not to concanavalin A-Sepharose 4B. All of the carbohydrate chains are N-linked. Enzymic removal of this carbohydrate decreased the Mr by approx. 15,000. The deglycosylated rat enzyme had the same mobility as native human factor D on SDS/PAGE, corresponding to an Mr of 24,500. N-Terminal sequence analysis of the first 30 amino acids of rat factor D highlighted the sequence similarity with human factor D (greater than 76%) and, in particular, with mouse adipsin (greater than 93%).