Prosthetic groups peptide link

All the complexes consist of several subunits (Table 2) complex I has a flavin mononucleotide (FMN) prosthetic group and complex II a flavin adenine dinucleotide (FAD) prosthetic group. Complexes I, II, and III contain iron-sulphur (FeS) centers. These centers contain either two, three, or four Fe atoms linked to the sulphydryl groups of peptide cysteine residues and they also contain acid-labile sulphur atoms. Each center can accept or donate reversibly a single electron. 

Describe, using a suitable example, each of the following (a) a prosthetic group, (b) a peptide link, (c) a S-S bridge and (d) the tertiary structure of a protein. 

Covalently bound prosthetic groups of proteins have been obtained in good yields from enzymatic hydrolyzates. Tables XV list several conjugated proteins that have been exhaustively degraded with enzymes. In each case prosthetic groups of the parent protein were isolated from the enzymatic hydrolyzates and were found to be linked to amino acid or peptides. 

Biochemical analyses of the assembly of the ergopeptines in C. purpurea have shown that ergopeptines are the products of an enzyme complex consisting of two nonribosomal peptide synthetase (NRPS) subunits (55). NRPSs generally exhibit modular structures, with each module responsible for the addition of an amino acid or other substituent. A typical module includes an adenylation (A-) domain, a thiolation (T-) domain (also known as a peptidyl carrier protein domain), and a condensation (C-) domain. The A-domain specifies the amino acid or other carboxylic acid substituent, and activates by it by an ATP-dependent adenylation reaction. The activated substituent then forms a thioester with the 4 -phosphopan-tetheine prosthetic group in the adjacent T-domain. Finally, the C-domain links the substituent to the next substituent in the chain. In a multimodular NRPS protein, the order in which substituents are added corresponds to the arrangement of modules from its N- to C terminus. 

Biotin is linked to the enz3une protein by a peptide bond to the -ainino group of a lysyl residue hence, it represents a prosthetic group. Charging biotin with carbon dioxide is an endergonic process requiring the assistance of ATP. 

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