PROTEINS 43
proteins from which they were derived. The authors stated that proteolytic O^18
labeling enabled a shotgun approach for proteomic studies with capability for
quantifi cation of the amount of a given protein in a complex mixture. The
authors proposed this method as a useful tool for comparative proteomic
studies of very complex protein mixtures. In other proteomic experiments, the
Fenselau group studied Bacilli mixtures [ Bacillus cereus strain T, Bacillus glo-
bigii strain 9372, wild - type Bacillus subtilis strain EMG 168, and Bacillus
thuringiensis subs. Kurstakistrain HD - 1 (ATCC 33679)], 11a developed a
method for quantitative determination of heme for forensic characterization
ofBacillus spores, 11b and developed another method for the characterization
of enterobacteria in mixtures [ E. coli ATCC 25404 (strain K12), Enterobacter
cloacae, Erwinia herbicola (also known as Pantoea agglomerans ), and Salmo-
nella typhimurium (strain 98 - 9176)], 11c all using the mass spectrometric
method called MALDI - TOFS (matrix - assisted laser desorption/ionization
time - of - fl ight mass spectrometry). This method is further described in Section
3.7.3.
Research in the Fenselau laboratory uses proteomics to study groups of
cellular proteins that may be responsible for acquired drug resistance. Acquired
drug resistance (ADR), causes chemotherapeutic agents to lose effectiveness
over time. In one study, Fenselau and coworkers examined the abundance
changes between proteins in (1) a drug susceptible MCF - 7 breast cancer cell
line and (2) a cell line (from the same parent line) exhibiting resistance to the
anticancer drug mitoxantrone. The study identifi ed 15 proteins with signifi cant
changes — including receptors, adhesion proteins, proteins involved in amino
acid uptake or in glucose uptake. 12a Alterations in the mitochondrial proteome
of adriamycin resistant MCF - 7 breast cancer cells were found in a 2D - gel
based comparative proteomic analysis conducted in 2006 by the same
group. 12b
In addition to the stable isotope labeling (^18 O versus^16 O) of proteins for
quantifi able proteomic analyses as described above, chemical approaches to
the protein - labeling problem have developed in great variety. These so - called
“ affi nity tags ” can be used to label specifi c side chain groups such as sulfhydryl
or amino groups, active sites for serine and cysteine hydrolases and many
others. This active research area has been reviewed recently by A. Leitner and
W. Lindner in a Proteomics article entitled: “ Chemistry meets proteomics: The
use of chemical tagging reactions for MS - based proteomics. ”^13
2.2.4 Protein Function, Enzymes, and Enzyme Kinetics,
Protein functions and interactions are infi nitely varied in biological species —
one of the major problems associated with complete classifi cation of any
proteome. Proteins may transport substances: myoglobin and hemoglobin (dis-
cussed in Chapter 7 ) transport oxygen, and carbon dioxide, in mammalian
blood. Proteins called enzymes catalyze necessary biochemical reactions. The
active site of an enzyme contains those amino acids that come in direct contact
