Figure 4 (A) Picture of a Genomic Solutions ProMS automated MALDI sample spotter and (B-C) enlarged views of a MALDI sample target mounted in the unit, showing the result of spotting analyte on the target.

A small aliquot of the digest solution can be directly analyzed by MALDI-MS to obtain a peptide map. The resulting sequence coverage (relative to the entire protein sequence) displayed from the total number of tryptic peptides observed in the MALDI mass spectrum can be quite high, i.e., greater than 80% of the sequence, although it can vary considerably depending on the protein, sample amount, and so forth. The measured molecular weights of the peptide fragments along with the specificity of the enzyme employed can be searched and compared against protein sequence databases using a number of computer searching routines available on the Internet. An example of such an exercise is depicted in Figure 5 and is discussed further in Section IDLE.