Dityrosine, 3,4-dihydroxyphenylalanine (DOPA), and radical formation from tyrosine residues on milk proteins with globular and flexible structures as a result of riboflavin-mediated photo-oxidation

TY - JOUR

T1 - Dityrosine, 3,4-dihydroxyphenylalanine (DOPA), and radical formation from tyrosine residues on milk proteins with globular and flexible structures as a result of riboflavin-mediated photo-oxidation

AU - Dalsgaard, Trine K

AU - Nielsen, Jacob H

AU - Brown, Bronwyn E

AU - Stadler, Nadina

AU - Davies, Michael Jonathan

PY - 2011/7/27

Y1 - 2011/7/27

N2 - Riboflavin-mediated photo-oxidative damage to protein Tyr residues has been examined to determine whether protein structure influences competing protein oxidation pathways in single proteins and protein mixtures. EPR studies resulted in the detection of Tyr-derived o-semiquione radicals, with this species suggested to arise from oxidation of 3,4-dihydroxyphenylalanine (DOPA). The yield of this radical was lower in samples containing β-casein than in samples containing only globular proteins. Consistent with this observation, the yield of DOPA detected on β-casein was lower than that on two globular proteins, BSA and β-lactoglobulin. In contrast, samples with β-casein gave higher yields of dityrosine than samples containing BSA and β-lactoglobulin. These results indicate that the flexible structure of β-casein favors radical-radical termination of tyrosyl radicals to give dityrosine, whereas the less flexible structure of globular proteins decreases the propensity for tyrosyl radicals to dimerize, with this resulting in higher yields of DOPA and its secondary radical.

AB - Riboflavin-mediated photo-oxidative damage to protein Tyr residues has been examined to determine whether protein structure influences competing protein oxidation pathways in single proteins and protein mixtures. EPR studies resulted in the detection of Tyr-derived o-semiquione radicals, with this species suggested to arise from oxidation of 3,4-dihydroxyphenylalanine (DOPA). The yield of this radical was lower in samples containing β-casein than in samples containing only globular proteins. Consistent with this observation, the yield of DOPA detected on β-casein was lower than that on two globular proteins, BSA and β-lactoglobulin. In contrast, samples with β-casein gave higher yields of dityrosine than samples containing BSA and β-lactoglobulin. These results indicate that the flexible structure of β-casein favors radical-radical termination of tyrosyl radicals to give dityrosine, whereas the less flexible structure of globular proteins decreases the propensity for tyrosyl radicals to dimerize, with this resulting in higher yields of DOPA and its secondary radical.

KW - Amino Acid Motifs

KW - Animals

KW - Cattle

KW - Dihydroxyphenylalanine

KW - Free Radicals

KW - Lactoglobulins

KW - Milk Proteins

KW - Oxidation-Reduction

KW - Protein Conformation

KW - Riboflavin

KW - Serum Albumin, Bovine

KW - Tyrosine

U2 - 10.1021/jf200277r

DO - 10.1021/jf200277r

M3 - Journal article

C2 - 21696221

SN - 0021-8561

VL - 59

SP - 7939

EP - 7947

JO - Journal of Agricultural and Food Chemistry

JF - Journal of Agricultural and Food Chemistry

IS - 14

ER -