Rapidly quantitative analysis of γ-glutamyltranspeptidase activity in the lysate and blood via a rational design of the molecular probe by matrix-assisted laser desorption ionization mass spectrometry.

Gamma-glutamyl transpeptidase (GGT) plays an important role in cellular glutathione/cysteine homeostasis and is a potential tumor biomarker. Herein, we report a rationally designed molecular probe (Aq-ECG) for rapid and quantitative analysis of GGT activities via matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). The probe is a water-soluble molecule consisting of an UV-absorptive aromatic anthraquinone (Aq) and a GGT cleavable glutathione (ECG) via one-step thiol-ene reaction covalently linked together. The function of anthraquinone part is not only to increase molecular mass of the target ions after GGT catalyzed cleavage enabling the report ions appearing in higher m/z region avoiding matrix ion interference, but also to remarkably enhance the report ions ionization efficiency. Additionally, the aromatic Aq part can be selectively captured by home-made magnetic graphene oxide materials and separated the targets from complex mixtures. Under optimized conditions, when employing an Aq linked methylated-glutathione (Aq-ECA) as the internal standard, the GGT activity amount can be quantified in a linear range of 1-50 U/L with r2 > 0.99. Applying this probe the GGT levels in human serum samples from both healthy and liver cancer patients have been readily detected; the results were consistent with those determined by an enzyme-linked immunosorbent assay. This method was also successfully applied for the detection of endogenous GGT amounts in different tumor/normal cells and the inhibition capability of sodium butyrate (an anticancer drug) to GGT activity. Thus, a simple, sensitive and cost/time economic method has been demonstrated for accurately quantitative GGT activity assay and screening of its inhibitors/anticancer drugs via the using of a functional molecular probe. This method is also widely applicable for other protease activity analysis by the replacement of reaction/report part of the probe.