Relationship between biotin-binding proteins from chicken plasma and egg yolk

Area of Science:

• Biochemistry
• Avian Physiology
• Nutritional Science

Background:

• Biotin is an essential vitamin crucial for various metabolic processes.
• Avidin, a biotin-binding protein found in egg white, is well-characterized.
• The transport mechanism of biotin in laying hens, particularly its delivery to oocytes, remains incompletely understood.

Purpose of the Study:

• To characterize the biotin-binding protein present in the plasma of laying hens.
• To compare the properties of plasma biotin-binding protein with egg yolk and egg white (avidin) biotin-binding proteins.
• To elucidate the potential role of plasma biotin-binding protein in biotin transport to the oocyte.

Main Methods:

• Biochemical characterization including heat-exchange studies for biotin-binding.
• Gel filtration chromatography (Sephadex G-100) to assess molecular weight.
• Ion-exchange chromatography (phosphocellulose) to determine ionic properties.
• Isoelectric focusing to determine isoelectric point (pI).
• Immunological assays (antiserum cross-reactivity and precipitin lines) to assess protein identity.

Main Results:

• Plasma and egg yolk contain a similar biotin-binding protein, distinct from avidin.
• Both proteins are saturated with biotin and require heat for [14C]biotin exchange.
• Molecular weight, ionic strength requirements, and isoelectric point (pI=5) are similar for plasma and yolk proteins, differing from avidin (pI=10).
• Plasma biotin-binding protein is immunologically identical to yolk biotin-binding protein.

Conclusions:

• The biotin-binding protein in laying hen plasma is biochemically and immunologically identical to the egg yolk biotin-binding protein.
• These findings suggest that plasma biotin-binding protein plays a crucial role in transporting biotin from the bloodstream to the developing oocyte.
• This mechanism ensures efficient delivery of biotin for egg formation.