Zinc and copper binding proteins in human milk

Area of Science:

• Biochemistry
• Human Nutrition
• Trace Element Metabolism

Background:

• Human milk is a vital source of essential trace elements like zinc and copper for infant development.
• Understanding the binding proteins and distribution of these minerals is crucial for assessing their bioavailability.
• Previous studies have indicated the presence of various binding fractions, but detailed characterization is ongoing.

Purpose of the Study:

• To fractionate and identify proteins that bind zinc and copper in human milk.
• To determine the distribution of zinc and copper among these identified binding compounds.
• To hypothesize on the factors influencing the distribution and potential bioavailability of these trace elements.

Main Methods:

• Ultracentrifugation was used to separate casein.
• Gel filtration and ion-exchange chromatography were employed to isolate other binding proteins.
• Gel electrophoresis was utilized for protein identification.
• Quantification of zinc and copper distribution across different fractions was performed.

Main Results:

• Casein bound 14% of total zinc and 28% of total copper.
• Serum albumin was identified as a binding protein, accounting for 28% of zinc and 39% of copper.
• A significant portion of zinc (29%) and copper (24%) was found in low molecular weight forms.
• Zinc (29%) and copper (9%) were also associated with the milk fat fraction.

Conclusions:

• Human milk contains multiple binding compounds for zinc and copper, including casein, serum albumin, low molecular weight fractions, and fat.
• The relative distribution of zinc and copper among these binding compounds is influenced by their concentrations and association constants.
• This distribution pattern may significantly impact the bioavailability of zinc and copper for the infant.