Chemical modification of proteins

Chemical modifications of proteins (enzymes) by reacting them with iV-acylimidazoles are a way of studying active sites. By this means the amino acid residues (e.g., tyrosine, lysine, histidine) essential for catalytic activity are established on the basis of acylation with the azolides and deacylation with other appropriate reagents (e.g., hydroxylamine). 

Cysteine is the most frequently used residue for selective chemical modification of proteins due to its relatively low abundance in proteins and the increased nucleophilicity of the thiol group relative to other natural amino acid side chains. The intrinsic selectivity is low unless no cysteine is present or unless all unwanted cysteines... 

Chemical modification of proteins — This can lead to denaturation and aggregation and reduce both specificity (increased nonspecific binding) and sensitivity (decreased ligand affinity). 

Chemical modification of proteins has been extensively studied over the years to identify which amino acids are involved in catalysis. Much less work has been carried out on its influence on enzyme stability. Chemical modification of proteins may yield stabilization, destabilization or no effect at all. Martinek and Berezin (1978) reported the dependence of the thermostability of chymotrypsin on the degree of alkylation of its amino groups up to 30% alkylation the stability rose slightly at 90% substitution stability increased markedly, with a maximum (110-fold) at 95% stability fell to nearly initial values when 100% amino groups were modified. (With these modifications, the optimum pH of the errzyme can change and one must therefore be cautious in comparing two different... 

S. (1976) Chemical Modification of Proteins Selected Methods and Analytical Procedures, Elsevier, New York... 

Means, G.E. and Feeney, R.E. 1971. Chemical Modification of Proteins. Holden-Day, San Francisco. 

Rademann, J. (2004). Organic protein chemistry drug discovery through the chemical modification of proteins. Angew. Chem. Int. Ed. 43, 4554-4556. 

Inada, Y., Matsushima, A., Hiroto, M., Nishimura, H., Kodera, Y. Chemical Modifications of Proteins with Polyethylen Glycols. Vol. 52, p. 129... 

The understanding and prediction of such effects and the development of milder and more selective synthetic transformations, applicable to the synthesis of highly complex structures or to the selective chemical modification of proteins, DNA, or even living cells will continue to be the challenge for current and future generations of chemists. 

McRobbie, I.M., Meth-Cohn, O. and Suschitzky, H. (1976) Tetrahedron Lett. 925. Means, G.E. and Feeney, R.E. (1971) Chemical Modification of Proteins, Holden-Day Inc., San Francisco. 

Nagaraj, R.H., Sarkar, P., Mally, A., Biemel, K.M., Lederer, M.O., and Padayatti, P.S. 2002. Effect of pyridoxamine on chemical modification of proteins by carbonyls in diabetic rats characterization of a major product from the reaction of pyridoxamine and methylglyoxal. Arch Biochem Biophys 402 110-119. 

M. U. Ahmed, E. B. Frye, T. P. Degenhardt, S. R. Thorpe, and J. W. Baynes, Nc-(Carboxyethyl)lysine, a product of the chemical modification of proteins by methylgly-oxal, increases with age in human lens proteins, Biochem. J., 1997, 324, 565-570. 

A mong the numerous special techniques that have been developed in recent years to assist the investigation and exploitation of protein structure, chemical modification of proteins has assumed a prominent role (1,2,3,4). A glance at the contents page of any modern biochemical journal bears witness to this. A specialized approach to research using chemical modification of proteins has developed and is used presently in fundamental studies of the structure and function of enzymes and other proteins as well as in studies related to industrial needs, foods, nutrition,... 

It is difficult to devise a precise system by which chemical modifications of proteins can be classified. A useful division is that between (a) those that are performed intentionally for specific purposes and (b) those that can be described as deteriorative or incidental to the processing, storage, or aging of protein-containing materials. 

Deteriorative chemical modifications of protein structure are found in nearly all biological systems and have been discussed at length in a recent symposium (12). They will be described only in outline here. (For an overview, see the article by Feeney (13)). 

The aim of this chapter is to describe briefly the progress and current status of the chemical modifications of proteins and how they are being applied to food, nutritional, and pharmacological sciences. In many instances, the subjects covered superficially here are covered in depth in other chapters in this volume. We hope that omissions will be understood sympathetically as due to the wide scope of the subject. 

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