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ANALYSIS OF PHOTO‐OXIDIZED AMINO ACIDS IN TRYPTIC PEPTIDES OF CALF LENS γ‐II CRYSTALLIN
Author(s) -
Hott J. L.,
Borkman R. F.
Publication year - 1992
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1992.tb02155.x
Subject(s) - amino acid , crystallin , tryptophan , histidine , peptide , chemistry , cysteine , methionine , biochemistry , amino acid analysis , eye lens , lens (geology) , biology , enzyme , paleontology
— Insoluble and crosslinked proteins and increased pigmentation in the eye lens are features of aging and cataracts. Determining the amino acids which are involved in insolubilization, crosslinking and visible light scattering will shed light on the mechanisms by which cataracts form. Calf lens γ‐II crystallin was irradiated at 295 nm, digested and separated into tryptic peptides. Additional tryptic peptides were found in the digest of irradiated γ‐II which were not present in the dark control digest. These peptides were identified by amino acid sequencing and shown to correspond to expected tryptic fragments of the protein, indicating more facile digestion in the UV‐irradiated protein than in dark controls. Amino acid analysis of the irradiated protein and peptides showed losses of histidine. methionine and cysteine residues as compared to control samples. Tryptophan, which is not detected by amino acid analysis, was also found to be reactive since losses in its fluorescence intensity were observed after irradiation. Some of the photochemically active amino acids had lower than expected responses in amino acid sequencing experiments. This suggested specific sites of photochemical activity in the various peptides. The evidence for peptide crosslinks is also discussed.

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