MALDI of Noncovalent Complexes

Within these boundary conditions, a number of reports have described the successful detection of several types of noncovalent complexes [113-118]. During the early days of MALDI, high-intensity signals of noncovalent protein complexes 

IR-MALDl enables comparably soft desorption processes and is, therefore, more appropriate for noncovalent complex analysis than UV-MALDl. This is reflected by the successful detection of intact double-stranded DNA as well as enzyme-oligosaccharide complexes in combination with glycerol as matrix which were not detectable or underwent significant fragmentation when UV-MALDI was employed [126, 127]. 

In more recent approaches, ionic liquid matrices have been used for the facilitated detection of intact noncovalent complexes, most probably due to the omitted requirement of intact complex incorporation into the matrix crystals [86]. 

Some aggravating circumstances such as the first-shot phenomenon can be circumvented by the accumulation of only first shots fired at fresh sample surfaces. As a consequence of these hindered conditions, numerous approaches regarding the investigation of noncovalent complexes use stabilizing chemical crosslinking between the complex partners in combination with high-mass M ALDI [122, 128, 129]. 

In summary, the use of MALDI to investigate noncovalent interaction is far less straightforward than typical applications for peptides and proteins under denaturing conditions. Success is not predictable, and careful control experiments must be implemented to differentiate specific from nonspecific interactions. 

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