Carbohydrates reactions, with proteins

NB The nomenclature is confused for glycosybUion and glycation. Over the past decades, the terminology has varied However, the nomenclature currently in favour is glycosybUion applies to carbohydrate reactions with proteins pre-translation while glycation is reserved for reactions post-translation. 

Glycation has been observed in a lyophilized formulation of relaxin in which a glucose adduct was identified.Formulation of recombinant human DNase with lactose in a spray-dried state resulted in the addition of lactose molecules to five of the six Lys in the protein.A similar reaction was observed in a lyophilized formulation of hGH in lactose. Because of the tendency of reducing sugars to undergo the Maillard reaction with proteins, they are not the carbohydrates of choice for use in formulations. 

Figure 25.7 Glycoprotein formation occurs by initial phosphorylation of the starting carbohydrate to a glycosyl phosphate, followed by reaction with UTP to form a glycosyl uridine 5 -diphosphate. Nucleophilic substitution by an -OH (or -NH2) group on a protein then gives the glycoprotein.

Virtually all energy released from the oxidation of carbohydrate, fat, and protein is made available in mitochondria as reducing equivalents (—H or e ). These are funneled into the respiratory chain, where they are passed down a redox gradient of carriers to their final reaction with oxygen to form water. 

Mucoproteins (See Section V).—Protein-carbohydrate compounds with relatively high protein or peptide content, the chemical reactions of which are predominantly protein, are known as mucoproteins. In general they do not coagulate on being heated in aqueous solution. All mucoproteins contain a hexosamine constituent. 

Figure 1.117 Glucosylamine derivatives can be prepared at the reducing end of glycans or other reducing carbohydrates by reaction with ammonium carbonate. The resultant amine derivative can be used to conjugate the carbohydrate with other proteins or molecules without disturbing the cyclic character of the reducing end.

The results obtained with this procedure are similar to those previously reported in the literature by Hangartner, Hagenguth et al and Zeman et al (4, 2, 5, 6). The major exception, being the complete lack of alkylated pyrazines and alkylated thiophenes. These odour-intensive compounds arise from the thermal decomposition of proteins and sulphur containing amino acids. They also develop in the thermally induced reaction of proteins with carbohydrates (Maillard reaction). The authors indicated above have demonstrated that these compounds are invariably produced during the thermal treatment of sludge, a process which is not used in this Authority. 

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