Vitellogenine

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Vitellogenins (lat. Vitellum , yolk ) in general are proteins that are produced by animals as precursors for lipoproteins and phosphoproteins. The place of further processing is different: in egg-laying invertebrates and vertebrates , the secreted vitellogenin is introduced into the egg cells by endocytosis and split with the help of cathepsin D ; the partial proteins serve as reserve substances for lipids ( lipovitin ) and phosphate ( phosvitin ); The latter is able to complex additional calcium and iron as a reserve for the embryo. The production of vitellogenin is stimulated by estrogens . Other homologues of vitellogenin are found in animals as a transport protein for triglycerides in the blood. This also includes, for example, the apolipoprotein -B-100 in humans. Mutations in the corresponding APOB - gene can cause serious hereditary damage in lipid metabolism.

Excerpt from the iron-binding protein phosvitin

Both the reserve substances in egg-laying animals and the aforementioned transport proteins have the vitellogenin domain in common, consisting of a superhelical domain at the N -terminal end and several large open beta-sheets . Only the reserve substances in egg-laying animals are referred to as vitellogenins in the narrower sense. When Haushuhn three are orthologous genes known, one for each isoform encoding . Vitellogenin-1 contains 1850, vitellogenin-2 1912 and vitellogenin-3 347 amino acids. The latter only serves as a precursor for phosvitin. The roundworm Caenorhabditis elegans, on the other hand, produces six different vitellogenin isoforms, all of which have around 1,600 amino acids.

Use as an estrogen test

The gene that controls vitellogenin production is also present in males. It is only activated by 17β-estradiol and other active substances. Juvenile and male animals react very sensitively, sometimes with sex reassignment, to the intake of hormones or substances with effects analogous to DDT or PCB .

The vitellogenin test can be used in egg-laying animals to demonstrate the estrogenic activity of a substance. For example, male fish are used and the amount of vitellogenin produced is measured. This then determines the estrogenic effectiveness based on the comparison with known substances .

Phosvitin saponification

Phosvitin in the egg yolk

The binding of iron in egg yolks of hens' eggs is carried out by the protein phosvitin. This contains a particularly large amount of the amino acid serine . The amino acid sequence is formed from pure blocks of phosphoserine residues (6-8 residues), which are interrupted by mixed blocks of other amino acids. The hydroxyl group in serine is often esterified with phosphoric acid . The resulting compound is called phosphoserine 1 and contains many anionic groups . This enables the phosphoserine residues to complex iron (2) ions with the formation of 1 . If a hen's egg is cooked too long , the iron ions from 1 are initially released, leaving the esterified serine units 2 behind. Finally, the phosphoric acid esters are split off from the protein by saponification , so that the serine blocks 3 are reformed . Hydrogen phosphate is also formed . The iron ions diffuse to the interface between egg yolk and egg white , where, together with hydrogen sulfide , they form the characteristic, black-brown edge.

Individual evidence

  1. ↑ UniProt P55155 , UniProt P87498 , UniProt P04114
  2. ↑ Swiss Institute of Bioinformatics (SIB): PROSITE documentation PDOC51211. Vitellogenin domain profile. Retrieved August 14, 2011 .
  3. ^ A b Günter Fred Fuhrmann: Toxicology for natural scientists: Introduction to theoretical and special toxicology. Springer, 2006, ISBN 978-3-8351-0024-4 , p. 343
  4. ↑ Hans-Hinrich Kaatz: Initiation and regulation of the vitellogenin synthesis in the queen bee (Apis mellifica L.) . Tübingen 1985, DNB  860721612 (dissertation, University of Tübingen).
  5. ↑ Interpro: Vitellogenin, superhelical , Vitellogenin, open beta-sheet
  6. ↑ UniProt P87498 , UniProt P02845 , UniProt Q91025
  7. ↑ Robert Guderian, Günter Gunkel: Handbook of environmental changes and ecotoxicology. Vol. 3, Aquatic Systems. Biogenic stress factors - organic substance inputs - behavior of xenobiotics. Springer, 2000, ISBN 978-3-540-66188-7 , pp. 364ff
  8. ^ André Leisewitz: Reproductive damage and environmental hormones - a new environmental problem? (PDF; 653 kB) , 1996, Greenpeace e. V.
  9. ^ Karl Höll, Andreas Grohmann: Water: use in the cycle, hygiene, analysis and evaluation. 8th edition, Walter de Gruyter, 2002, ISBN 978-3-11-012931-1 , p. 559
  10. ↑ Entry on phosvitin. In: Römpp Online . Georg Thieme Verlag, accessed on June 4, 2020.
  11. ↑ Roth, K. (2010): Chemical delicacies . 1st edition, Weinheim: Wiley-VCH. P. 34f.