There isn't a single perfect noun for "protein" in the same way that we have "sugar" for carbohydrates. However, depending on the context, some options could be:

* Protein: This is the most common and straightforward term.

* Protein molecule: This emphasizes the molecular structure of protein.

* Polypeptide: This is a more technical term referring to the long chains of amino acids that make up protein.

* Amino acid chain: Another technical term highlighting the building blocks of protein.

* Proteid: This is an older, less common term for protein.

The best choice really depends on the specific context and the intended audience.