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Characterization of phosphorus content of biological samples by ICP-DRC-MS: potential tool for cancer research

Bandura, D.R., Ornatsky, O.I., Liao, L.

Phosphorus and sulfur are detected as phosphorus oxide and sulfur oxide ions (PO+ and SO+), produced by oxidation reactions with O2 performed in the reaction cell of the inductively coupled plasma dynamic reaction cell mass spectrometer (ICP-DRC-MS), at sub-ng mL−1 detection limits. This allows pM mL−1 detection of phospho-proteins, with S used as an internal standard (see ref. 9). The method was applied to digests (in HCl) of in-vitro tyrosine kinase assays, both as an evaluation of kinase autophosphorylation and phosphorylation of substrate. Detecting the phosphorus/sulfur ratio (via measured PO+/SO+) in cell cultures is shown to provide a distinguishable difference between malignant cell lines and primary cultures. The PO+/SO+ ratio for human colorectal adenocarcinoma (CRC) tissue samples compared with matched normal (N) tissue samples from the same patients is shown to be higher, at (PO+/SO+)CRC/(PO+/SO+)N = 1.75 ± 0.18 (n = 4). Samples used in this analysis were of needle biopsy amounts (0.2–0.5 mg), with a greater than 70% tumor burden in CRC. The phospho-protein phosvitin is detected directly from dried one-dimensional polyacrylamide gels using laser ablation ICP-MS by detecting phosphorus at sub-nM amounts. The phosphorus detection limit for direct ablation, assessed from ablating gel doped with P and blank gel, is 0.6 µg g−1 in gel. Direct detection of sulfur from the gels is obscured by the high sulfur background for the blank gels, which is attributed to the sulfur-containing catalysts used in polymerization and to sodium dodecyl sulfate (SDS) used for protein denaturing.

Citation

Bandura, D.R., Ornatsky, O.I., Liao, L. "Characterization of phosphorus content of biological samples by ICP-DRC-MS: potential tool for cancer research" Journal of Analytical Atomic Spectrometry (2014): 96–100