Digestion completeness of microwave-assisted and conventional trypsin-catalyzed reactions.

Microwave-assisted proteolytic digestion often yields misscleaved peptides, attributed to incomplete hydrolysis reactions between enzymes and substrates. The number of missed cleavages is an important parameter in proteome database searching. This study investigates how various factors affect digestion processes. Optimum conditions for microwave-assisted digestion (50 mM Tris buffer, 30 min at 60 degrees C, and enzyme to protein molar ratio of 1:5) were determined. The digestion products obtained from eight standard proteins were characterized based on matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). Experimental results indicate that the digestion temperature, reaction time, enzyme to substrate ratio, and digestion buffer affect the number of misscleaved peptides and incomplete digestion percentages. Although all protein molecules in a sample could be digested into peptides within a few minutes under microwave irradiation, longer reaction times or methods to maximize the enzyme activity should be considered if digestion completeness is a major concern.

The electrochemical behavior of p-benzenediol on a self-assembled monolayers Pt electrode modified with N-(2-mercapto-1,3,4-thiadiazol-5-yl)-N'-(4-substituted-arylacetyl) urea.

Two novel N-(2-mercapto-1,3,4-thiadiazol-5-yl)-N'-(4-substituted-arylacetyl) urea compounds have been synthesized, characterized by NMR and MS, and used as self-assembly reagents to form self-assembled monolayers (SAMs) on Pt electrodes. The modified electrodes were characterized by electrochemical methods. The electrochemical behavior of p-benzenediol at the SAMs electrodes was investigated. It was found that the electrochemical response to p-benzenediol is controlled by diffusion and can be electrocatalyzed to obtain more symmetrical redox peaks and higher voltammetric current response at the SAMs electrodes, with a peak separation of 80 mV. For p-benzenediol the process at the SAMs electrodes is quasi-reversible with a rate constant of 0.6742 s-1. The SAMs electrodes have been used to determine p-benzenediol by differential pulse voltammetry. The peak current was linear for concentrations of p-benzenediol in the range 1x10(-7)-5x10(-4) mol L-1 and the detection limit was 4.0x10(-8) mol L-1. The SAMs electrodes were used to determine p-benzenediol in real photographic developer and in a synthetic waste water sample; the standard addition recovery was in the range 96.6-100.4%.