Mass spectrometric analysis of the products from the isotopomeric cationic intermediates in the solvolysis of 1,2-dianisyl-2-p-(2H3)methoxyphenyl[2-13C]vinyl bromide in 70% HOAc – 30% H2O

1983 ◽  
Vol 61 (9) ◽  
pp. 2159-2164
Author(s):  
Choi Chuck Lee ◽  
Xian-Da Yu ◽  
Charles Y. Fiakpui

Solvolyses were carried out with 6.0 mM doubly labeled 1,2-dianisyl-2-p-(2H3)methoxyphenyl[2-13C]vinyl bromide in 70% HOAc – 30% H2O in the presence of 0, 1, 5, 10, or 400 molar equivalents of added NaOAc. The distributions of products derived from the 4 possible isotopomeric trianisylvinyl cationic intermediates were determined from the mass spectra of the isotopomeric dianisyl ketones obtained from degradation of the reaction products, the spectra being obtained by the chemical ionization technique in order to minimize possible complications by multiple fragmentations. The mass spectrometrie results obtained showed agreement with previously obtained 14C scrambling data and with the 13C scramblings obtained in the present study using 13C nmr. Increasing amounts of added NaOAc had the effect of decreasing the extents of scrambling from 1,2-anisyl shifts as previously observed. However, the formation of products from all 4 possible doubly labeled isotopomeric trianisylvinyl cations definitely demonstrated the occurrence of successive 1,2-anisyl shifts in the trianisylvinyl cation, and the detection of such successive shifts was not possible in previous work using a singly labeled substrate. The observed distribution of products derived from the 4 isotopomeric cations could be calculated assuming various contributions from equilibrations among these isotopomeric cations, and the mechanistic implications of the results are discussed.

2003 ◽  
Vol 30 (2) ◽  
pp. 239-252 ◽  
Author(s):  
ES Jacoby ◽  
AT Kicman ◽  
RK Iles

Metabolism of the human chorionic gonadotrophin (hCG)- and LHbeta-subunits (hCGbeta, LHbeta) terminates with the urinary excretion of core fragment (hCGbetacf, LHbetacf) molecules that retain antigenic shape and constituent N-linked carbohydrate moieties. We have previously demonstrated the resolved mass spectra of hCGbetacf, from which the carbohydrate moieties present at two N-linked glycosylation sites were identified. LHbetacf was subjected to the same mass spectrometric analysis. As LHbeta shares 82% homology with hCGbeta but possesses only one glycosylation consensus site a simpler spectral fingerprint of LHbetacf glycoforms was expected. LHbetacf was reduced with dithiothreitol and analysed by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry. Glycoforms were predicted by subtracting the peptide mass from the m/z values of the observed peaks and then sequentially subtracting the masses of the monosaccharide residues of hCGbeta N-linked carbohydrates reported in the literature. The mass spectra of LHbetacf revealed a broad single peak ranging from m/z 8700 to 10 700. Following reduction, this peak was replaced by a set of partially resolved peaks between m/z 4130 and 5205 corresponding to glycosylated forms of the peptide LHbeta6-40. A peak at m/z 4252.2 corresponded to the non-glycosylated peptide LHbeta55-93. Remaining peaks indicated that the pooled sample comprised a wide set of glycoforms, contained LHbetacf with two N-linked carbohydrate moieties and indicated evidence of further glycosylation due to amino acid substitution in polymorphic variants. This is evidence that a single nucleotide polymorphism alters the post-translational modification of a protein and hence its structural phenotype.


2017 ◽  
Vol 56 (36) ◽  
pp. 9993-9998 ◽  
Author(s):  
Pattasuda Duangkaew ◽  
Shuhei Inoue ◽  
Tsunehiro Aki ◽  
Yutaka Nakashimada ◽  
Yoshiko Okamura ◽  
...  

1976 ◽  
Vol 48 (3) ◽  
pp. 491-493 ◽  
Author(s):  
I. C. Wang ◽  
H. S. Swofford ◽  
Philip C. Price ◽  
D. P. Martinsen ◽  
S. E. Buttrill

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