Dissociation of human chorionic gonadotropin into its free subunits is dependent on naturally occurring molecular structural variation, sample matrix and storage conditions.
Measurement of human chorionic gonadotrophin (hCG) is used in many areas of clinical medicine. Recent interest has focused on the stability of this molecule and its fragments during sample storage. In the body hCG is degraded and removed by specific metabolic processes which begin while the molecule is in the bloodstream. In particular, the receptor binding loop of the beta subunit is cut or 'nicked', initiating a catabolic cascade. Furthermore, the extent and nature of glycosylation is believed to have a significant influence on this process. In these studies we incubated seven glycoforms of hCG, each with different degrees of 'nicking', in phosphate-buffered saline, serum, defibrinated blood and urine from healthy non-pregnant women, under varying conditions. Degradation was expressed as the molar increase in free beta subunit. Under all conditions there was a steady dissociation of hCG over time, the process being more rapid at higher temperatures. 'Nicked' hCG dissociated more rapidly than did non-'nicked' hCG. Glycosylation reduced the rate of dissociation. Dissociation was most rapid in urine and buffer solutions, and slowest in serum and defibrinated blood.
Butler
S A
SA
Department of Obstetrics and Gynaecology, Royal London School of Medicine and Dentistry, West Smithfield, London, UK.
Cole
L A
LA
Chard
T
T
Iles
R K
RK
D006063:Chorionic Gonadotropin / Q000097:blood / Q000737:chemistry* / Q000276:immunology; D003429:Cross Reactions; D005260:Female; D006031:Glycosylation; D006801:Humans; D011487:Protein Conformation; D013048:Specimen Handling; D013696:Temperature; D013997:Time Factors
D006063:Chorionic Gonadotropin