Measuring the peptides in individual organelles with mass spectrometry

New sampling protocols combined with matrix-assisted laser desorption/ioniz ation time-of-flight mass spectrometry (MALDI-TOF MS) allow the assay of si ngle dense core vesicles. Understanding the packaging of vesicles is import ant as vesicles are the quanta of information for intercellular communicati on. Using vesicles from the exocrine atrial gland of Aplysia californica as the model, a wide range of bioactive peptides are detected within each ves icle. Although the expression of the egg-laying hormone gene family of type 1 atrial gland cells has been previously examined, chemical characterizati on of individual 1-2 mu m diameter vesicles demonstrates that products from several genes are colocalized. The mass sensitivity of MALDI MS can be fur ther improved to enable the analysis of even smaller subcellular organelles .