G-Glycosylation

While electrospray is used for molecules of all molecular masses, it has had an especially marked impact on the measurement of accurate molecular mass for proteins. Traditionally, direct measurement of molecular mass on proteins has been difficult, with the obtained values accurate to only tens or even hundreds of Daltons. The advent of electrospray means that molecular masses of 20,000 Da and more can be measured with unprecedented accuracy (Figure 40.6). This level of accuracy means that it is also possible to identify post-translational modifications of proteins (e.g., glycosylation, acetylation, methylation, hydroxylation, etc.) and to detect mass changes associated with substitution or deletion of a single amino acid. 

Plants contain to some extent less bioavailable forms of vitamin B6, e.g., glycosylates, or biologically inactive metabolites, e.g., e-pyridoxin-lysin-complexes. In addition, the release of vitamin B6 from foods rich in fiber is assumed to be delayed. The bioavailability of vitamin B6 from animal-derived foods is therefore overall higher than from plant-derived foods. Good dietary sources of vitamin B6 include chicken, fish, pork, beans, and pulses [1]. 

Post-translation modification Changes that occur to proteins after peptide-bond formation has occurred, e.g. glycosylation and acylation. 

The microreactor in Fig. 1 demonstrated the ability to rapidly obtain comprehensive information about a given chemical transformation, e.g., glycosylation, over a wide range of conditions (Ratner et al. 2005). Experimental efforts and time were considerably reduced and valuable starting materials conserved by combining the microreactor with auto-... 

Other modified forms deamidated, isomerized, mismatched S-S linked, oxidized, or altered conjugated forms (e.g., glycosylation, phosphorylation). 

G. Glycosylation of 3-methoxy-2-pyridyl 2,3.4-tri-O-benzoyl-P-D-glucopyranoside with 2,3,4.6-tetra-O-benzyl-p-D-glucopyranosyl 2-thiopyridylcarbonate 459... 

Within the amino acid sequence there may be specific sequences which act as signals for the post-translational processing of the protein (e.g. glycosylation or proteolytic processing see Topic H5). 

Vankayalapati, H, Jiang, S, Singh, G, Glycosylation based on glycosyl phosphates as glycosyl donors, Synlett, 16-25, 2002. 

Cipolla, L, Lay, L, Nicotra, F, Panza, L, Russo, G, Glycosyl sulfates as glycosyl donors. Tetrahedron Lett., 35, 8669-8670, 1994. 

Tingoli, M., Temperini, A., Testaferri, L., Tiecco, M., Resnati, G. Glycosylation reaction using anomeric selenoxides. Carbohydr. Lett. 1998, 3, 3946. 

Escherichia coli Easy to grow in large-scale volumes Transcriptional and translational control well known Successfully used in the manufacture of insulin, interferon and human somatotropin Difficult to achieve export of some proteins into growth medium Degradation of small proteins by proteases Unable to undertake most post-translational modifications, e.g. glycosylation Many proteins retained in the cytoplasm as insoluble aggregates... 

Deamidated, isomerized, mismatched S-S linked, oxidized, or altered conjugated forms (e.g., glycosylation, phosphorylation) may be detected and characterized by chromatographic, electrophoretic, and/or other relevant analytical methods (e.g., HPLC, capillary electrophoresis, MS, and CD). 

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