Quantification of specific proteins depends on separation by chromatography
or electrophoresis followed by chemical detection schemes such as staining
and fluorophore adhesion. Chemical exchange of short-lived isotopes, parti
cularly sulfur, is also prevalent despite the inconveniences of counting ra
dioactivity. Physical methods based on isotopic and elemental analyses offe
r highly sensitive protein quantitation that has linear response over wide
dynamic ranges and is independent of protein conformation. Accelerator mass
spectrometry quantifies long-lived isotopes such as C-14 to subattomole se
nsitivity, We quantified protein interactions with small molecules such as
toxins, vitamins, and natural biochemicals at precisions of 1-5%. Micro-pro
ton induced X-ray emission quantifies elemental abundances in separated met
alloprotein samples to nanogram amounts and is capable of quantifying phops
phorylated loci in gels. Accelerator-based quantitation is a possible tool
for quantifying the genome translation into proteome.