Replacing alanine by which amino acid will increase UV absorbance by protein at 280 nm wavelength?

Amino acids do not absorb visible light and thus are colorless. However, tyrosine, phenylalanine, and especially tryptophan absorb high-wavelength (250-290 nm) ultraviolet light. Because it absorbs ultraviolet light about ten times more efficiently than either phenylalanine or tyrosine, tryptophan makes the major contribution to the ability of most proteins to absorb light in the region of 280 nm. Ref: Harper’s illustrated biochemistry. 30th edition page no: 21-22