ANALYSIS OF THE MICROHETEROGENEITY OF THE GLYCOPROTEIN CHORIONIC-GONADOTROPIN WITH HIGH-PERFORMANCE CAPILLARY ELECTROPHORESIS

Human chorionic gonadotropin (hCG) is a heteromeric glycoprotein hormone with a molecular mass of ca. 38 000. The carbohydrate side chains terminate with sialic acid and account for roughly 30% of the mass of the hormone. Glycoforms of hCG have been routinely identified with conventional methods of isoelectric focusing or chromatofocusing and exhibit varied bioactivity. In the present report, high-performance capillary electrophoresis (HPCE) was used to separate the glycoforms of hCG and its subunits. Optimal conditions for obtaining near-baseline resolution of the glycoforms were 25 mM borate, pH 8.8 containing 5 mM diaminopropane. The samples were separated in a 100 cm fused-silica capillary with an internal diameter of 50 mu m at 25 kV and 28 degrees C. In its native form, hCG migrated in less than 50 min as 8 distinct, highly resolved peaks. In the absence of diaminopropane, hCG migrated as a single, broad peak. When analyzed individually, the alpha subunit separated into four peaks and the beta subunit resolved as seven peaks. The two subunits could also be separated when the heterodimer was incubated in 0.25% trifluoroacetic acid for 1 h prior to injection into the capillary. To illustrate the potential clinical application of this technique, four different sources of hCG were analyzed. The number of different isoforms was constant among the four samples; however, the relative concentration (amounts) of the isoforms varied. These results illustrate the potential utility of HPCE in the clinical diagnostic analysis of hCG microheterogeneity.