Side chain polarity Reset Display the imino group as Ball & Stick. Instead of a primary amino group, Pro has a secondary amino group; Pro is sometimes called an imino acid. Compare the saturated five-membered ring of Pro to the side chain imidazole ring of His. Some facts on L-proline. Abbreviation: Pro. One-letter code: P. Molecular mass: 115 daltons. Side chain (or R-group) features: Structural formula: Formula: -(CH2)3-NH- (cyclic); Category: hydrophobic; neutral pKa: none. Return to image of Pro.
Some facts on L-proline.