Peptides sequencing studies

Many individual procedures have been devised which make use of isotopic labels to assist in particular peptide sequencing studies by mass spectrometry. Two further recent examples, in addition to those reported above, are mentioned here. 

Mass spectral fragmentation patterns of alkyl and phenyl hydantoins have been investigated by means of labeling techniques (28—30), and similar studies have also been carried out for thiohydantoins (31,32). In all cases, breakdown of the hydantoin ring occurs by a-ftssion at C-4 with concomitant loss of carbon monoxide and an isocyanate molecule. In the case of aryl derivatives, the ease of formation of Ar—NCO is related to the electronic properties of the aryl ring substituents (33). Mass spectrometry has been used for identification of the phenylthiohydantoin derivatives formed from amino acids during peptide sequence determination by the Edman method (34). 

Crystallographic studies imply that although little sequence homology exists between the different protease cleavage sites, what is conserved is the shape that they adopt within the active site of the enzyme (Prabu-Jeyabalan et al. 2002). This shape has been termed the substrate envelope and represents the consensus volume overlapping the majority of the substrates. Most likely, HIV-1 protease recognizes a particular peptide sequence as being a substrate by a combination of accessibility and the shape the sequence can adopt. 

Attaching some short peptidic sequences to adamantane makes it possible to design novel antagonists. The bradykinin antagonist, which is used as an anticancer agent, is an example. The adamantane-based peptidic bradykinin analog was utilized in strucmre-activity relationship (SAR) studies on the bradykinin receptors and showed a potent activity in inhibition of bradykinin-induced cytokine release and stimulation of histamine release [142]. 

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