Cysteine activation

J Kovac, GL Mayers, RH Johnson, RE Cover, UR Ghatak. Racemization of amino acid derivatives. Rate of racemization and peptide bond formation of cysteine active esters. J Org Chem 35, 1810, 1970. 

R. S. Czemuszewicz and E. M. Maes, Biological Applications of Resonance Raman Spectroscopy Copper-Cysteinate Active Sites, in Education in Advanced Chemistry , eds. A. M. Trzeciak, P. Sobota, and J. J. Ziolkowski, Wydawnictwo Poznanskie, Poznan-Wroclaw, Poland, 2000, Vol. 7, p. 67. 

Independent of the thiol protecting groups used in the synthesis of cysteine peptides, the facile racemization of the Cys residue has been recognized as a serious problem since the early days of peptide chemistry (see Section 1.2.1.2 and Vol. E22b, Section 7.4).It is well established that N,S-protected cysteine active esters are unusually prone to racemization via a C -proton-abstraction mechanism in the presence of excess amines (Scheme More... 

Heterosubunits of FXlll-A B dissociate with formation of FXIII-A and FXIII-B in the presence of calcium ions. At the last stage of the process also proceeding in the presence of Ca FXIII-A undergoes the most significant conformational transformations that lead to exposure of cysteine active center with enzyme FXIII-A formation [4]. Removing of FXIII-B from the complex is of essential importance for Ca Mependent transformation of FXIII-A2 to FXIII-A2 [35]. Transformation of nonactive FXIII-Ajto FXIII-A2 is accompanied by significant changes in the subunits stmcture [2]. In consequence of such stmctural transformations... 

This class of reactions has been investigated further and extended in a new direction by Fruton and his collaborators. Fruton digested ben-zoylglycineamide with cysteine-activated papain in the presence of N Ha. At all stages before complete hydrolysis, the amide radical in the unhydrolyzed benzoylglycineamide was found to be partially replaced by the from the medium. Eventually the substrate is practically... 

Bergmann s observations (7-11) indicated that analogous exchange reactions can occur with proteases and peptidases. But it had not been proved. The proof and extension in new directions came from the work of Fruton and his collaborators. One of the first experiments reported (60) was as follows. Benzoylglycineamide was digested with cysteine-activated papain in the presence of At all stages before complete hydrolysis... 

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