My initial encounter with Mass Spectrometry as a new scientific and technical discipline was before I started my Ph.D. training. I went to the Jean-Claude Promé's laboratory in Toulouse to analyse peptides obtained by thermolysin digestion of rat/mouse/pig neuronal tubulins. Neuronal tubulins had been found to be extensively polyglutamylated at their C-terminus and we were trying to determine the number of glutamyl residues that were condensed onto the C-terminal tail of alpha-tubulins purified from mammal brain.

At that time the MALDI and ESI ions sources were not yet popular (these experiments date back to the early nineties), and Jean-Claude was analysing my peptides using a magnetic sector mass spectrometer equipped with a LSIMS source. Although we had to make a chemical derivatization of each sample prior to analysis (which is no more required with MALDI and ESI sources), I was just amazed by the efficiency of the method and the level of detail into which we could go with a simple set of mass spectra.

I later had a collaboration with Prof Jean-Marie Schmitter, who then was at Laboratory of biochemistry of the Ecole polytechnique-X, near Paris (he now is in Bordeaux). He was using a MALDI-TOF instrument (a Fisons instrument, if I recall correctly). We wanted to take a look at a highly heterogeneous protein (telokin) preparation that I was purifying from chicken gizzard (a smooth muscle). While we never coud get anything interesting out of these analyses, that experience has been extremely valuable to me: I was learning analytical biochemistry the hard way, that is, the way that you experience when you try hard to get some signal out of some analyte you *know* is there in the sample, and that signal never comes.

Later, my Ph.D. lab (Jean Rossier's lab, at the Ecole supérieure de Physique et Chimie industrielles de la Ville de Paris, ESPCI) got a MALDI-TOF mass spectrometer (that was a Perseptive Voyager reflectron-TOF model). There, I could put my own hands on the instrument and I have to admit that was the period in which the mass spec virus caught me. We were, with Jean-Pierre LeCaer, Jean Mary and Virginie Redeker, the masters of the place, sharing time on that spectrometer day and night. I rapidly specialized in night mass spectrometry...

Of course, one of the first samples I deposited onto the MALDI plate was the telokin protein preparation we failed to analyse at Jean-Marie Schmitter's facility. I did not get any signal, once again. However, because *I* knew how carefully the protein was purified (not enriched, but truly purified), I could not accept that such a sheer amount of protein could not provide a significant signal. I decided I would stop stacking fractions from multiple chromatography runs so as to deposit always greater amounts of protein on the MALDI plate: I decided to run the other way, to dilute the protein. I remember I got a wonderful signal when I diluted the protein preparation we used to analyse with no result by a factor of 70!

This learning that using too much sample basically amounted to not using enough of it was very important to me. That experience certainly embodies the whole concept of sample preparation: care should be taken to prepare the sample in such a manner that the analytical step provides as much an informative data set as possible. You might read about of that sample preparation stuff here.

The following are some examples of mass spectrometry-using biochemical/bioanalytical projects that I have been involved in:

• Characterization of the molecular diversity of neuronal tubulins and of smooth muscle telokin;
• Characterization of the 3D topology of the yeast ATP synthase;
• Analytical biochemistry of protein commplexes showing a specific affinity for a cognate DNA sequence;
• Characterization of the molecular reactivity of human centrin2 in presence of oxidative species;
• Characterization of the molecular mechanism of inhibition of peptidoglycan-related enzymatic activities by the beta-lactam imipenem.