# What are usable Sum formulas for Proteins?

I'm looking for something like this: $C_{13}H_{25}O_7N_3S$ . Obviously it's not about knowing the exact shape or composition of a specific protein, but knowing the relative contents of major chemical components - not the absolute amounts.

I have several issues with the stated formula:

• I found this in some forum, but without a source
• Nitrogen content would be 11% by weight (per the formula), typical conversion factors used to calculate Protein content by measureing Nitrogen suggest values from 15% - 19% (equivalent to conversions factors 5.2 to 6.6). Something is wrong.

What are other, similiar sum formulas that account at least for the elements stated above and that are in use?

I'm trying to calculate the sulphur load of biological feedstocks for biogas plants. One assumption is that a large portion of Sulphur is bound in proteins. Protein content data (as calculated from total-N) is readily available. Knowing the S-content of Protein (or rather the N-S ratio) would allow me to check this hypothesis with one of the few data points I have for Sulphur contents of the feedstocks that interest me.

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Why not start with amino acid chemical formulas and join the amino acids together to make proteins? Of course, this explores all the possibilities - proteins within our genome are only a subset, but this should give upper and lower limits. – dd3 Mar 20 at 16:08
Or you could could get the FASTA sequences for the exons in your organism of interest and figure out the chemical composition of the proteins they encode. What organism are you interested in? – dd3 Mar 20 at 16:10
Why do you think something is wrong? 11% is not that far away from 15-19%. There are thousands of different proteins in our organism, so it really depends which one you get. – nico Mar 20 at 16:36
The downvote (was not cast by me) is probably because: 1) what does "nutrients" mean in this context? 2) What exactly do you need? The chemical formula you are posting could conceivably describe a small peptide but not an entire protein (unless it is a very very small one). 3) Protein sizes vary enormously, what kind of formula are you looking for? The average content in H,O,N and C in proteins? 4) Where do you get the 15-19% values? I don't see that in the page you linked to. 5) What exactly are you trying to do, why do you want this formula? – terdon Mar 21 at 14:49
Hi mart, I would say the edit was better, but (to me) you still don't seem clear about what you need. Considering sulfur in proteins, only cysteine (Cys) and methionine (Met) use S, and a subset of proteins are sulfonated. The proportion of Cys/Met in proteins varies widely, so 11-19% seems reasonable, and maybe even on the high end. Also keep in mind proteins are not static entities in a cell, they are always in flux, being broken down and synthesized. I'm not certain you can reduce it to a static chemical formula. – leonardo Mar 21 at 22:40
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