Food Science Factoids!
"Non-Protein" Amino Acids
#1 of 4: I learned this week that there are amino acids that do not form into polymers to create proteins. They are literally called "non-protein building block amino acids." (You'd think there'd be a shorter name.)
One of these natural amino acids is the very powerful antioxidant I always emphasize, found in black garlic. I didn't realize that this antioxidant has the two defining chemical-groups that are in all amino acids: (1) an amino group -NH2, and (2) a carboxylic acid group -COOH.
So a molecule that is an amino acid doesn't necessarily have to form into proteins!
Why the garlic plant (Allium sativum) forms this powerful antioxidant, "Sulfur-Allyl-Cysteine" (SAC) is to have a storage repository/reservoir of the molecule: alliin. When a garlic bulb is bruised (such as from an insect), the plant will convert the alliin to allicin, the pungent and volatile aroma chemical with strong antimicrobial, antifungal, and insect-repelling properties. The plant can call on reserves of SAC to form more alliin, like Sergeant Al Powell in Die Hard calling in for backup at Nakatomi Plaza. (great movie scene, by the way.)
SAC in black garlic: a non-protein building block amino acid, and a powerful antioxidant!
There are so many other natural non-protein building block amino acids. Here are some:
#2 of 4 Plant Defense Amino Acids:
L-DOPA (L-3,4-dihydroxyphenylalanine): A precursor to dopamine in humans, but in plants like the velvet bean (Mucuna pruriens), it is used as a potent defense chemical against insects. It is also famously used as a drug to treat Parkinson's disease.
beta-Alanine: A structural component of pantothenic acid (Vitamin B5) and a key ingredient in muscle carnosine. Plants often use it as a stress-response molecule against dehydration or high salinity.
Canavanine: A structural mimic of the standard amino acid arginine. Many plants synthesize canavanine as a defense mechanism; when an insect eats the plant, it inadvertently incorporates canavanine into its proteins instead of arginine, which causes the insect's proteins to fold incorrectly and malfunction.
#3 of 4 Precursors to gases or signaling molecules,
1-Aminocyclopropane-1-carboxylic acid (ACC): The vital precursor for the ripening hormone ethylene in plants like bananas.
Ornithine: A key player in the urea cycle in animals, which helps dispose of excess nitrogen. It is also a precursor for the synthesis of polyamines, which are essential for cell division and growth.
Citrulline: Another essential intermediate in the urea cycle. It is also famously found in high concentrations in watermelons. It plays a role in the production of nitric oxide, which helps dilate blood vessels.
gamma-Aminobutyric acid (GABA): A non-protein amino acid that acts as a primary inhibitory neurotransmitter in the human brain. It is also heavily produced by plants (like tea leaves) as a stress-response mechanism.
#4 of 4 Another important Sulfur-Containing Amino Acid
Homocysteine: A derivative of the standard amino acid methionine. While it is a natural intermediate, elevated levels in humans are often clinically monitored because they can indicate metabolic imbalances.