Ascorbate enhances copper transport from ceruloplasmin into human K562 cells

Area of Science:

• Biochemistry
• Cell Biology
• Nutritional Science

Background:

• Ceruloplasmin (Cp) is a major copper-transporting protein in human plasma.
• Cellular copper uptake mechanisms are crucial for various biological processes.
• The role of ascorbic acid in modulating copper metabolism is not fully understood.

Purpose of the Study:

• To investigate copper (Cu) uptake from human ceruloplasmin (Cp) into K562 erythroleukemic cells.
• To determine the influence of ascorbic acid on this copper transfer process.
• To explore the implications for cellular copper metabolism and enzyme synthesis.

Main Methods:

• Preparation of nondenatured 67Cu-labeled ceruloplasmin (67Cu-Cp).
• Incubation of 67Cu-Cp with K562 cells at 37°C.
• Assessment of copper uptake and dissociation resistance.
• Evaluation of ascorbic acid and D-isoascorbate effects on copper uptake.
• Analysis of 67Cu incorporation into Cu-Zn superoxide dismutase (Cu-Zn SOD).

Main Results:

• 67Cu rapidly transferred from Cp to K562 cells, resisting mild acid washing.
• Copper uptake rate was proportional to Cp concentration.
• Ascorbate significantly enhanced 67Cu uptake (at least fourfold).
• D-Isoascorbate showed similar enhancement, highlighting the importance of reducing potential.
• Approximately 20% of absorbed 67Cu was incorporated into Cu-Zn SOD, unaffected by ascorbate.

Conclusions:

• Ascorbic acid, via its reducing potential, plays a critical role in facilitating copper uptake from ceruloplasmin into K562 cells.
• Copper availability may not be the sole rate-limiting factor for Cu-Zn SOD synthesis in these cells.
• Findings suggest potential relevance to vitamin C deficiency and cellular copper metabolism.