Hydrolysing large molecules to reveal amino acids

Consider Oxytocin:

I am asked to hydrolyse Oxytocin and reveal 5 amino acids which are the result of this hydrolysis.

I must admit I have no idea where to begin. I know that generally amino acids are on the form of $\ce{NH_2-CH-R-COOH}$ so perhaps looking at these double bonds to oxygen may be a starting point as I assume they will become the acid group? But I really don't know how to move forward from there!

• It's highly irrelevant, but it would be nice of you to put the source of the images. Some of them may even be subjects to copyright. – M.A.R. Feb 9 '15 at 17:12
• It's from a local newspaper in Denmark. I think it's a public image and therefore ok to use. – Paze Feb 9 '15 at 17:31
• Oh, just wanted to remind. In this case, I don't think it's necessary. – M.A.R. Feb 9 '15 at 17:38
• Just to be sure: Do you ask for a real experimental procedure or just for a hint on how to identify (visualize) the different amino acids on paper? – Klaus-Dieter Warzecha Feb 9 '15 at 17:48
• looks like more than 5 amino acids to me – DavePhD Feb 9 '15 at 17:53

You are on the right track. $\ce{NH_2-C(H)R-COOH}$ is the formula for an alpha amino acid, one where the amino group of the molecule is attached to a carbon atom one carbon atom away from the carboxylate carbon. This is the most common type of amino acid found in biochemistry. (A beta amino acid would be $\ce{NH_2-C(H)R^2-C(H)R^1-COOH}$).

When amino acids condense into a polymer or oligomer they do so by forming peptide bonds, also called amide bonds.

$\ce{R^1COOH + NH2R^2 -> R^1CONH2R^2 + H2O}$

So to find the places in oxytocin that would be hyrolyzed into amino acids, look for individual carbon atoms that are attached to both (i) an oxygen atom via a double bond and (ii) a nitrogen atom while (iii) not being attached to any other heteroatoms. (Item (iii) is generally necessary to exclude other functional groups such as carbamides or carbamates, but these groups are not found in oxytocin.) For oxytocin, your impulse to look just at carbon double-bonded to oxygen (item (i) only) is OK, but be warned that this procedure is not precise enough in general, because molecules with e.g. ketone moieties will have C=O bonds but will not be hydrolyzed.

The red-circled amino group is a free amino group: the carbon attached to it is not bound to a carbonyl oxygen, so it is not a place where hydrolysis will happen. (However, look one carbon atom to the left of C atom attached to the circled N....)

@DavePhD is right; there are more than five amide bonds in oxytocin. I think there are a total of ten. Eight are the result of amide bond formation between alpha amino acids and two are the result of amide bond formation between an acid side chain and unsubstituted ammonia.

• Thanks, I have identified the carbon atom to the left of the one attached to the free amino group. I see that it is double bonded to an oxygen but I don't see how it is bonded to a nitrogen? Also is it not bound to the CCHNH group straight to its left? I'm also looking at various double bound oxygens and the carbons attached to them seem all to be attached to either a hydrogen or a carbon, therefore heterocarbons? – Paze Feb 10 '15 at 8:12
• Hi Bjarni, I worry you are being mislead by structural abbreviations. HNHC is a weird shorthand for H2N-C. Maybe it would be easiest for you to find a better picture/structure of oxytocin to use for your problem. – Curt F. Feb 10 '15 at 14:34