Edward A. Dratz

Laser desorption time-of-flight mass spectra of peptides and proteins, as well as of lower molecular weight analytes, have been obtained by using a pulsed nitrogen UV laser (337 nm) to irradiate mixtures of 2-150 microns graphite particles and solutions of the analytes in glycerol. Protonated analytes as well as abundant alkali cation adducts were observed. Carbon cluster ions, Cn+, typically had a low abundance but dominated the mass spectrum at elevated laser powers. In spectra of a cytochrome c tryptic digest, all but one of the tryptic peptides were easily observed. Spectra of low molecular weight analytes dissolved in glycerol are very similar to FAB spectra of the same glycerol solution with added alkali salts. However, in many peptide and protein spectra, glycerol ion abundances are very low, and the alkali ions dominate the spectra at low mass. These spectra may correspond to wet and dry surface desorption conditions, respectively. The best spectra of the larger molecules were observed under dry conditions. In these initial experiments, we have obtained a sensitivity in the pico- to nanomole range and a mass resolution of about 300. The signal intensity is as good as that in conventional MALDI, and under optimal conditions, few background peaks appear, even at low mass.

The idea that mediates is a conceptual thread that has woven through biological research for decades. The molecules in biological superstructures such as membranes are vectorially oriented in both space and time. As with the code provided by the Rosetta Stone, if we could learn to recognize the meaning of the vectorial arrows and follow them through their causally interconnected junctions, we would indeed understand how function is mediated through the dynamic structure of the component molecules. Few processes have as many structural signposts suggesting causal interpretation as does vertebrate vision. Rod and cone outer segments are so structurally specialized for the translation of optical into ionic events that even their enormous concentration of mitochondria (that are essential for driving the large light-modulated current in photoreceptors) are relocated in an adjacent chamber. The rod disk and cytoplasmic transduction apparatus of the receptor outer segment is axially repeated a thousand times with great precision. At the level of a single axial unit, which consists of a disk membrane