Protein absorbances come from 3 sources →化* transiton 1s very intense at190m Peptide bond n-n* transition is weak as it is symmetry forbidden it forms a shoulder on the一>几* transition(emax" 100)at 210-220 nm Aromatic Amino acids-- most useful Phe 8250=400 symmetry forbidden T->T* Tyr274=14007->兀* Trp 280=4500 at least 3 different transitions. A280 is one of the most commonly used methods to measure protein concentration(aside from colorimetric methods such as the Lowry or Bradford dye binding assays), but this method is obviously very sensitive to differences in amino acid composition These transitions can change with pH; especially Tyr Prosthetic Groups Nucleotides ->e.g FMN, NAD Retinal etcProtein absorbances come from 3 sources Peptide Bond Aromatic Amino Acids -- most useful Phe e250 = 400 symmetry forbidden p --> p* Tyr e274 = 1400 p --> p* Trp e280 = 4500 at least 3 different transitions. A280 is one of the most commonly used methods to measure protein concentration (aside from colorimetric methods such as the Lowry or Bradford dye binding assays), but this method is obviously very sensitive to differences in amino acid composition. These transitions can change with pH; especially Tyr Prosthetic Groups Nucleotides --> e.g. FMN, NAD Heme Cu Retinal etc