Human Chorionic Gonadotropin

The effects of oligosaccharide branch chains on the hydrodynamic behavior of reduced glycopolypeptides was examined by gel chromatography in random coil producing solvents. This entailed a comparison of the gel chromatographic behavior in the presence of concentrated guanidinium chloride of 16 glycopolypeptides of known physical and chemical properties to that of regular polypeptides. For most of the glycopolypeptides employed, the presence of oligosaccharide branches sufficiently perturbed the dimensions of the unfolded glycopolypeptide such that its effective hydrodynamic radius was the same as that of a linear polypeptide of the same total mass. For this reason, gel chromatography in random coil producing solvents appears to be the most reliable empirical method to obtain a first approximation of the molecular weight of a glycopolypeptide. Glycopolypeptides rich in N-acetylneuraminic acid, and thus possessing low isoionic points, exhibited more pronounced deviations in their electrophoretic behavior in the presence of 8 M urea than those glycopolypeptides whose ionic properties were similar to those of the polypeptide standards employed.

Section: Methodsmentioning

confidence: 99%

Behavior of glycopolypeptides with empirical molecular weight estimation methods. 2. In random coil producing solvents

Leach¹,

Collawn²,

Fish³

1980

“…The placental hormone, human chorionic gonadotropin (hCG1), is a glycoprotein comprised of two nonidentical subunits, a and ß, held together by noncovalent bonds (Morgan and Canfield et al, 1971). The subunits, which can be dissociated in acid or in concentrated solutions of urea, have been purified and their amino acid sequences determined (Carlsen et al, 1973;Bellisario et al, 1973;Morgan et al, 1975). The individual subunits have little or no biological activity (Catt et al, 1973) but can be recombined at neutral pH to yield biological activity comparable to that of the native hormone (Swaminathan and Bahl, 1970;Aloj et al, 1973a;Morgan et al.…”

mentioning

confidence: 99%

Kinetics of recombination of the subunits of human chorionic gonadotropin. Effect of subunit concentration

Kc¹,

Bd²,

Edelhock³

1976

The rate of formation of human chorionic gonadotropin from its alpha and beta subunits has been measured at neutral pH and 37 degrees C as a function of subunit concentration, using the fluorescence probe, 1,8-anilinoaphthalene-sulfonate (ANS), to monitor the reaction. The subunits were prepared by acid dissociation of the intact hormone (pH less than or equal to 2, 37 degrees C). Following neutralization, the rate of appearance of ANS fluorescence was identical with the rate of recovery of receptor binding activity and both of these properties were completely recovered. Kinetic data obtained over a 100-fold range of subunit concentrations (1.5 to 146 muM) were not compatible with a simple second-order reaction scheme, but required at least one additional step. The data were best fit by a model in which the subunits reversibly form an intermediate complex (alpha + beta in equilibrium alphabeta) which then undergoes a conformational rearrangement to form the native structure (alphabeta leads to H). Ultraviolet difference absorption measurements suggest that most of the change in the environment of the tyrosyl residues occurs during this second step.

“…Prior studies (Carlsen et al, 1973;Morgan et al, 1975) have established the linear amino acid sequence of ß-hCG, but the positions of the disulfide bridges have not yet been determined due to the difficulty in obtaining specific cleavages resulting in peptides that maintain intact disulfide bonds. Under the conditions employed in the present study, the ß-mercaptoethanol reduced three to four of the six disulfide bonds present in the ß subunit of hCG.…”

Section: Discussionmentioning

confidence: 99%

“…Eightypercent of the sequence of the first 115 amino-terminal residues of the ß subunit of hCG are identical to those found in the ß subunit of LH Parlow, 1973, 1974;Closset et al, 1973; Sairam and Li, 1973). In addition, the ß subunit of hCG has an additional 30 amino acid residues in the carboxyl-terminal portion of the molecule which are not shared by LH (Carlsen et al, 1973;Morgan et al, 1975). Therefore, anti- Abbreviations used: hCG, human chorionic gonadotropin; LH.…”

mentioning

confidence: 99%

Location of major antigenic sites of the β-subunit of human chorionic gonadotropin

Swaminathan¹,

Braunstein²

1978

Self Cite

Purified beta subunit of human chorionic gonadotropin (hCG) was partially reduced with beta-mercaptoethanol, carboxymethylated, and digested with chymotrypsin. The peptides were isolated by high-voltage electrophoresis and paper chromatography. Five major disulfide-containing peptides were isolated, and their location in the parent molecule was established by amino acid composition and amino- and carboxy-terminal analyses. All of these peptides inhibited the binding of 125I-labeled hCG by anti-beta hCG serum. The inhibitory effect of these peptides was lost when their disulfide bonds were reduced and alkylated. Synthetic carboxy-terminal peptides were not inhibitory. Based on these data it is concluded that a major antigenic site of hCG resides in the region of residues 21-23 with a disulfide bond connecting cysteine-23 or -26 with the cysteines at positions 72 or 110.