SPECTROSCOPIC INVESTIGATIONS OF BOVINE LENS CRYSTALLINS .1. CIRCULAR-DICHROISM AND INTRINSIC FLUORESCENCE
SPECTROSCOPIC INVESTIGATIONS OF BOVINE LENS CRYSTALLINS .1. CIRCULAR-DICHROISM AND INTRINSIC FLUORESCENCE
复制标题
DOI：
10.1021/bi00537a022
复制
发表时间：
1982-01-01
期刊：
影响因子：
2.9
通讯作者：
CHAKRABARTI, B
中科院分区：
文献类型：
--
作者：
LIANG, JN;CHAKRABARTI, B
Circular dichroism (CD) and intrinsic fluorescence measurements were carried out to study the secondary and tertiary structure of the lens proteins .alpha.-, .beta.H-, .beta.L- and .gamma.crystallins. CD spectra of crystallins in the far-UV region, typical of the .beta. conformation of a protein, show some variation in .beta. content, which may not have any significant biological correlation. .beta.H- and .gamma.-crystalline show a band at 235 nm which probably originates from an interaction between a peptide amide transition and a transition of aromatic amino acid residues. Near-UV CD spectra (250-310 nm) of these proteins, which arise mostly from aromatic amino acid residues, differ considerably from each other. The differences cannot be attributed to variations in the content of aromatic amino acid residues; they reflect the extent of the interactions between these residues (.mu.-.mu. coupling) and their difference in tertiary structure. Attempts were made to assign the CD bands, as much as possible, on the basis of absorption and pH-dependent CD spectra. There is no significant contribution of disulfide bonds to the near-UV CD, as indicated by the lack of difference in the dichroic behavior between dithiothreitol-reduced and untreated samples. Near-UV CD spectra indicate that tryptophan residues in .gamma.-crystallin are mostly buried in a hydrophobic environment; in .alpha.-crystallin, they are least buried; similarly, tyrosine residues in both .beta.-crystallins are in more polar environments than are .alpha.- and .gamma.-crystallins. Emission maxima and quantum yield values of the fluorescence of lens crystallins suggest that exposed tryptophan residues in these proteins are in the .alpha. > .beta.H .apprxeq. .beta.L > .gamma., which is consistent with near-UV CD results. Because of efficient energy transfer from tyrosine to tryptophan in these proteins, tyrosine fluorescence can be observed only when it is measured in guanidine hydrochloride (Gdn-HCl). Unlike emission maxima, values of the quantum yields in Gdn-HCl are not uniform, indicating the sensitivity of tryptophan fluorescence to the residual 3-dimensional structure or to the persisting interaction between tryptophan residues and other side chains even after denaturation.
