Profiling Kinase Activities by Using a Peptide Chip and Mass SpectrometryThis work was supported by the National Science Foundation. D.-H.M. was supported by the Burroughs Wellcome Fund Interfaces Program.

Herein we describe a strategy that combines peptide chips with matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry (MS) to evaluate kinase activities rapidly and semi-quantitatively. We have already shown that monolayers of alkanethiolates on gold are wellsuited as substrates for MALDI-TOF MS, and could be used to measure enzyme activities and to perform high-throughput screenings. 2] A significant aspect of this approach—which we term SAMDI (self-assembled monolayers for MALDI) MS—is that it avoids the use of labels, greatly simplifying the formatting of assays. Herein we establish two important