In this study, incubation-induced alterations in the protein secondary structures of egg yolk
and its major fractions (granules, plasma, and lowdensity lipoproteins [LDL]) were monitored during the
first 8 d of embryogenesis using Fourier transform infrared spectroscopy (FTIR) and isoelectric focusing
(IEF). Two factors potentially connected with egg yolk protein secondary structure changes were evaluated,
i.e., the pH value of incubated egg yolk, and phosvitin, an important egg yolk protein assumed to play an important role in hematopoiesis as the iron carrier during early embryogenesis. However, neither the significant increase in pH value (6.07 to 6.92) of egg yolk during incubation of fertilized eggs, nor the release of iron from phosvitin were found to be directly related to the changes in protein secondary structure in egg yolk and its fractions. FTIR showed that the protein conformation in whole egg yolk, granules,
and LDL was stable during incubation, but separate
evaluation of the plasma fraction revealed considerable
changes in secondary structure. However, it is unlikely
that these changes were provoked by structure
changes of the proteins originally present in plasma;
instead, the physiological influx of albumen into the
yolk sac was expected to play an important role in
the protein modifications of egg yolk, as was shown
both by FTIR and IEF of the water-soluble egg yolk
proteins. Moreover, FTIR was used to determine the
naturally occurring proportions (%) of the secondary
structure elements in egg yolk and its 3 fractions on
d 0 of incubation. The granules fraction mainly consisted
of a mixture of inter- and intramolecular β-sheets
(57.04% ± 0.39%). The plasma fraction was found to
consist mainly of α-helices (43.23% ± 0.27%), whereas
LDL was composed almost exclusively of intramolecular
β-sheets (67.36% ± 0.56%) or β-turns, or both. On
the other hand, whole egg yolk was mainly composed
of intermolecular β-sheets (39.77% ± 0.48%), potentially
indicating molecular
In this study, incubation-induced alterations in the protein secondary structures of egg yolkand its major fractions (granules, plasma, and lowdensity lipoproteins [LDL]) were monitored during thefirst 8 d of embryogenesis using Fourier transform infrared spectroscopy (FTIR) and isoelectric focusing(IEF). Two factors potentially connected with egg yolk protein secondary structure changes were evaluated,i.e., the pH value of incubated egg yolk, and phosvitin, an important egg yolk protein assumed to play an important role in hematopoiesis as the iron carrier during early embryogenesis. However, neither the significant increase in pH value (6.07 to 6.92) of egg yolk during incubation of fertilized eggs, nor the release of iron from phosvitin were found to be directly related to the changes in protein secondary structure in egg yolk and its fractions. FTIR showed that the protein conformation in whole egg yolk, granules,and LDL was stable during incubation, but separateevaluation of the plasma fraction revealed considerablechanges in secondary structure. However, it is unlikelythat these changes were provoked by structurechanges of the proteins originally present in plasma;instead, the physiological influx of albumen into theyolk sac was expected to play an important role inthe protein modifications of egg yolk, as was shownboth by FTIR and IEF of the water-soluble egg yolkproteins. Moreover, FTIR was used to determine thenaturally occurring proportions (%) of the secondary
structure elements in egg yolk and its 3 fractions on
d 0 of incubation. The granules fraction mainly consisted
of a mixture of inter- and intramolecular β-sheets
(57.04% ± 0.39%). The plasma fraction was found to
consist mainly of α-helices (43.23% ± 0.27%), whereas
LDL was composed almost exclusively of intramolecular
β-sheets (67.36% ± 0.56%) or β-turns, or both. On
the other hand, whole egg yolk was mainly composed
of intermolecular β-sheets (39.77% ± 0.48%), potentially
indicating molecular
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