Spectroscopic Studies of Lipoproteins

Electronic spectroscopy provides an important technique for assessing protein concentration and structure, and, in proteins, the most important intrinsic structural probes are the aromatic amino acids phenylalanine, tyrosine, and tryptophan, with the latter being most important. This chapter describes the protein structure using several methods including measuring the fluorescence spectrum, polarization, quenching of intensity and lifetime, and energy transfer to suitable donors. The absorption spectra of purified proteins may be used to quantify their concentration according to the summation method of Edelhoch that permits one to calculate the A₂₈₀ of any apolipoprotein from its amino acid composition. Fluorescence is a very sensitive method; however, the level of detection is largely a function of the type of instrument employed and the purity of the solvent. The chapter suggests that the characteristic absorption and fluorescence of apolipoproteins are useful in their detection, quantification, characterization, and structural analysis. The rapidity with which photometric measurements can be made favors their use in the routine analysis of apolipoproteins.