Ellman reagent can be used to quantitate the amount of free thiol present in a protein or other molecule:
It reacts with the free thiol and releases a nitrocarboxythiophenolate, which is bright yellow. You can then quantitate it with a UV-vis.
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Pyridines and thiols are two of the stinkiest kinds of compounds you can come across in chemistry. You'd think if you put them together in a molecule, you'd have something nasty. Oddly, you don't:
The lablels on bottles of chemicals with warnings always make me smile. One often-joked about example is the bottles of chemicals labeled "Flammable (US) / Highly Flammable (Europe)," which makes you feel smug if you're on my side of the pond.
Ammonium thioglycolate is the ammonium salt of thioglycolic acid. Having a thiol (R-SH), thioglycolic acid is a decent reducing agent, particularly of disulfide bonds (R-S-S-R').