Abstract
Changes of serum proteins in rats with streptozotocin (STZ) -induced diabetes were analyzed by two-dimensional electrophoresis in non-denaturing conditions ; marked decreases or increases of several specific proteins were detected. W e report here, characterizations of four of those proteins (P1to P4), that changed especially after STZ administration. P1, with pI 4.4, decreased, and P2-P4, with pI 4.7, 4.2 and 4.7, respectively, increased. All were glycoproteins. Both P2and P3were determined by sequential analysis of peptide fragments digested wii: h lysylendopeptidase to be T-kininogen. No sequences coinciding with P1or P4were found in the Protein Database. P4was believed to be an α2HS-glycoprotein from its two-dimensional electrophoretic position, but had no properties known to human α2HS-glycoprotein. Purified P1and rat serum showed a single precipitin line in the α1-region in immunoelectrophoresis. This suggests that purified P1is immunochemically homogeneous, and the only protein that reacts with anti-P1in rat serum is P1. Anti-P1formed a precipitin line against mouse serum and partially fused with rat P1, but did not react with human, dog, cattle or horse sera. Serum P1concentration in control rats was about 6 mg/ml, and decreased below 50 % within 3 weeks after STZ administration. The P1concentration recovered when blood glucose was controlled at its normal level with insulin, 3 weeks after STZ administration, and decreased again to original level when rats were again maintained without treatment. The changed P2-P4also recovered when blood glucose was controlled at its normal level, suggesting close relation with diabetes, or at least with blood glucose level, after STZ administration.
