Molecules of the Week

L-Glutamine and L-Arginine

September 25, 2017

We two amino acids can make a whale of a difference. What molecules are we?

L-Glutamine and L-arginine are classified as semi-essential or conditionally essential amino acids, which means that the human body can synthesize them under some health conditions but not others. Both are abundant in many foods.

Neither D-glutamine nor D-arginine is common in nature, so the L-amino acids are usually referred to without prefixes. In 1883, German chemists Ernst. Schulze and E. Bosshard isolated L-glutamine from the juice of sugarbeets. It is the most common amino acid in human blood and a key component of proteins.

In 1886, Schulze was also the first to isolate L-arginine, in this case from lupin seedlings. It is also an important amino acid in protein biosynthesis.

It turns out that a difference in occurrence between these two amino acids makes a huge difference in huge animals. This year, while examining the melanocortin system* of cetaceans, Roger D. Cone at the University of Michigan (Ann Arbor) and colleagues discovered that the two suborders of the sea mammals have different components at position 156 in the melanocortin-4 receptor. Glutamine is at this position in baleen whales, whereas toothed whales and dolphins contain arginine instead.

Cone’s group found that arginine in the receptor suppresses the beasts’ appetites relative to the glutamine-containing receptor. They believe that this difference contributes to the much larger sizes of baleen whales.

*The melanocortin system is an important regulator of metabolism, food intake, and fat storage.

Learn more about this week’s molecule from the CAS REGISTRY, which is searched using SciFinder®. Each record displays the registry number, index name and synonyms, bibliographic information, and more.

Molecule of the Week needs your suggestions!

If your favorite molecule is not in our archive, please send an email to The molecule can be notable for its current or historical importance or for any quirky reason. Thank you!

Molecule of the Week: 3d: L-Glutamine
Molecule of the Week: 2d: L-Glutamine

L-Glutamine Fast Facts

CAS Reg. No. 56-85-9
Molar mass 146.14 g/mol
Formula C5H10N2O3
Appearance White crystals or powder 
Melting point 185 ºC (dec.)
Water solubility 25 g/L

Molecule of the Week: 3d: L-arginine
Molecule of the Week: 2d: L-arginine

L-Arginine Fast Facts

CAS Reg. No. 74-79-3
Molar mass 174.20 g/mol
Formula C6H14N4O2
Appearance White crystals or powder
Melting point 244 ºC (dec.)
Water solubility 15 g/L

Stay Ahead of the
Chemistry Curve

Learn how ACS can help you stay ahead in the world of chemistry.