(To the tune of “Rudolph the Red-Nosed Reindeer”) / Recording by David Simmons
You know threonines, serines, and trusty aspartates
Cobalts, magnesiums, zincs and glutamates
But do you recall?
The best characterized enzymes of all
All serine proteases
Work almost identically
Using amino acid
Triads catalytically
First they bind peptide substrates
Holding onto them so tight
Changing their structure when they
Get them in the S1 site
Then there are electron shifts
At the active site
Serine gives up its proton
As the RE-ac-tion goes on
Next the alkoxide ion
Being so electron rich
Grabs peptide’s carbonyl group
Breaks its bond without a hitch
So one piece is bound to it
The other gets set free
Water has to act next to
Let the final fragment loose
Then it’s back where it started
Waiting for a peptide chain
That it can bind itself to
Go and start all o’er again
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