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I'd like to try a new spectroscopic technique to study enzymatic reactions (which reaction doesn't especially matter, something simple and with fast kinetics like catalase would do fine - I'm just trying to test the technique).

Unfortunately, for this technique to work, it is best if there aren't any aromatic amino acids around since it is entirely in the UV range.

I did a quick search in UniProt, and - somewhat surprisingly - there are very few proteins without aromatic amino acids, let alone any enzymes. The yeast protein sequences database contains zero(!) proteins with no aromatic AAs. The human database contains a few proteins (~20): for example many metallothioneins, proline-rich proteins, and HMG proteins have no aromatic AAs. No common enzymes turn up in that search.

Can anyone think of an enzyme - or perhaps a small catalytically active fragment of one - which has no aromatic amino acids?

If not - this is maybe a more general question - what makes aromatic amino acids apparently necessary for most enzymes?

P.S. The yeast results are: lowest aromatic AA content is 4% in vacuolar ATPase (many DNA/RNA polymerase subunits are also quite low); median is 11%, many common enzymes eg alcohol dehydrogenase, glutathione oxidoreductase etc fall in that range; highest is 24% in sterol methyl oxidase

UPDATE A thorough search of the RefSeq NR protein sequence db does turn up a whole lot of stuff, but it tends to be from weird species, mostly bacteria... eg oxaloacetate decarboxylase from Rubrivivax benzoatilyticus (which - maybe no surprise - eats aromatic compounds). It still seems like there is a strong selective pressure to incorporate aromatic AAs in enzymes

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    $\begingroup$ A control for your assumption of selective pressure would be info on proteins that lack other amino acids or groups thereof. I know that is not your particular concern, but…. And out of interest, is it possible to state what replaces the aromatics in the odd-balls you mention — can you do MSAs? If nobody else has done it you might even be able to publish your results. $\endgroup$ – David Nov 25 '18 at 20:00
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    $\begingroup$ The A280 peak in a protein absorption spectrum is mostly due to Trp residues (see for example, Protein Volumes and hydration effects by SJ Perkins). Perhaps you should consider using an enzyme without Trp? Such proteins are relatively rare but one well-know example is mitochondrial malate dehydrogenase. A non-enzymic example is microtubule-associated protein tau. $\endgroup$ – user1136 Nov 25 '18 at 23:05
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    $\begingroup$ See also how to measure and predict the molar absorption coefficient of a protein $\endgroup$ – user1136 Nov 25 '18 at 23:08

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