Zucker fa and La/N faf rats are widely studied models of genetic obesity and its complications. These two rodent models of obesity were utilized to search for a circulating protein marker for obesity. Plasma samples from both of these models of obesity were collected and analyzed via SDS-PAGE analysis. Two proteins were found which demonstrate differential expression between lean and obese rats. Both proteins demonstrated increased expression in the obese rats compared to the lean. One differentially expressed protein migrated on SDS-PAGE gels at 116 KD while the second migrated at 22 KD compared to molecular weight markers. The 22 KD protein also exhibited differential expression in plasma samples obtained from lean Zucker rats. Preliminary results from genetic backcrossing analysis point to a possible gene dosage effect with this protein. This coupled with the finding that the differential expression of this protein occurs before the onset of obesity in these rats may possibly make this an important circulating marker for obesity. These proteins were subjected to sequencing by Edman degradation. The protein migrating at 116 KD was identified as complement component C3 α chain, a pivotal member of the complement cascade, which is vital to the body’s immune system. The protein migrating at 22 KD was identified as apolipoprotein A-I, an important member of the body’s lipid transport system. Antibodies to these two proteins were purchased and the identities confirmed through Western blot analysis. Complement component C3 α chain may be important as it could serve as a circulating reservoir for the formation of acylation stimulating protein (ASP). Apolipoprotein A-I is an important protein component of high density lipoprotein particles which are important in cholesterol and lipid transport
