molecule of the day: benzamidine

The molecule of the day is benzamidine:

(PubChem)

It can be used to inhibit serine proteases, as in this paper.

molecule of the day: deoxypyridoxine

The molecule of the day is deoxypyridoxine:

It's a vitamin B6 antagonist, so my guess is that it inhibits sphingosine-1-phosphate lyase, because it uses pyridoxal

 
 as a cofactor, and I think that's why this paper includes it in their sphingosine kinase assay mix.  I think.

molecule of the day: quercetin

The molecule of the day is quercetin:

(PubChem)

It's an antioxidant.  It also apparently inhibits at least some diacylglycerol kinases.  The authors don't really discuss why they thought quercetin might inhibit their enzyme, but it's in the same section as the nucleotide analogs: maybe the flat fused rings targets the nucleotide binding site?

molecule of the day: tartaric acid

The molecule of the day is tartaric acid:

(PubChem)

It can be used to model Ins(1,3,4,5)P4

(PubChem)

in crystal structures.

molecule of the day: diisopropyl fluorophosphate

The molecule of the day is diisopropyl fluorophosphate:

(PubChem)

 Like other organophosphates (the most famous being sarin), it inhibits cholinesterases, but also lipases.  (And if the authors appreciated how dangerous this chemical they were working with was, they don't mention it in the methods.)

molecule of the day: leupeptin

The molecule of the day is leupeptin:

(PubChem)
It's a protease inhibitor produced by actinomycetes (source), which, as far as I can tell, is a polyphyletic group.

Molecule of the day: ouabain

The molecule of the day is ouabain:

It's derived from the seeds of Strophanthus gratus and inhibits the Na+/K+-ATPase (the Na+/K+ exchanger or sodium pump), and can therefore be used to distinguish among different enzymes' ATPase activities.