Proper nouns are usually capitalized - a primary-school lesson that all of us have learned.
Let's look at a substance found in a human body.
Arginine (/ˈɑrɡɪniːn/, abbreviated as Arg or R)1 is an α-amino acid. It was first isolated in 1886
Another one, this time a kind of poison
Solanine - Solanine is a glycoalkaloid poison found in species of the nightshade family (Solanaceae), such as the potato (Solanum tuberosum) and the tomato (Solanum lycopersicum).
Being a healthcare provider, I read several research papers, documents and webpages on enzymes or those sort of substances. They all have name, a proper name but none of those written content ever capitalize them. Why?
I also see some exceptions.
Hemp seeds are high in Arginine, an essential amino acid known to improve heart health and protect from heart disease.
But is it due to the comma there? As the following sentence is introducing what 'Arginine' is? But then, is there any rule that if you define a proper noun in the middle of the sentence, you capitalize its first letter and if you don't, you don't! I don't think so. :)