Biochemical properties of canine serum ferritin: iron content and nonbinding to concanavalin A

A sandwich enzyme-linked immunosorbent assay using H-subunit-rich canine heart ferritin as a standard has been developed for measuring canine serum ferritin which is H-subunit-rich. Serum ferritin concentrations in 51 normal dogs ranged from 143 to 1766 ng ml(-1), with a mean value of 479 +/- 286 (SD) ng ml(-1). Serum ferritin iron concentrations as determined by an immunoprecipitation technique ranged from 30.4 to 115.9 ng ml(-1) in 15 normal dogs with serum ferritin protein levels of 298 to 959 ng ml(-1). There was a significant linear correlation between the serum ferritin iron and protein levels (r=0.9441, P<0.001), and the mean iron/protein ratio of serum ferritin was 0.112 +/- 0.017. When canine sera were incubated with concanavalin A-Sepharose 4B, we observed the apparent binding of serum ferritin to concanavalin A. However, ferritin obtained by heat-treating the sera at pH 4.8 to remove the ferritin-binding proteins did not bind to the lectin. These results suggest that canine serum ferritin contains a considerable amount of iron but no concanavalin A-binding G subunit present in human serum ferritin.