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Erythrocyte membrane (Ca2+ + Mg2+)-ATPase in human protein-energy malnutrition

O O Olorunsogo1

  • 1Department of Biochemistry, College of Medicine, University of Ibadan, Nigeria.

Bioscience Reports
|June 1, 1989
PubMed

Insights

Erythrocyte membranes from children with kwashiorkor exhibit significantly reduced Ca2+-pumping ATPase activity and impaired calmodulin regulation compared to healthy children, indicating compromised calcium transport in this condition.

Area of Science:

  • Biochemistry
  • Cell Biology
  • Pediatric Nutrition

Background:

  • Kwashiorkor is a severe form of malnutrition characterized by edema, skin lesions, and fatty liver.
  • Calcium homeostasis is crucial for cellular function, and its regulation involves Ca2+-pumping ATPase (Ca2+ + Mg2+-ATPase) and the modulator protein calmodulin.
  • Erythrocyte membranes serve as a model for studying cellular transport mechanisms.

Purpose of the Study:

  • To investigate the functional status of Ca2+-pumping ATPase in erythrocyte membranes from children with kwashiorkor.
  • To assess the role of calmodulin in modulating the activity of Ca2+-pumping ATPase in kwashiorkor.
  • To compare the kinetic properties (ATP affinity, Ca2+ affinity, calmodulin affinity) of the enzyme between kwashiorkor and healthy children.

Main Methods:

  • Preparation of calmodulin-free ghost membranes from erythrocytes of kwashiorkor and healthy children.
  • Assay of Mg2+-dependent Ca2+-pumping ATPase specific activity and kinetic parameters (Km for ATP, Ca2+, calmodulin affinity).
  • Determination of enzyme activity dependence on calcium concentration in the absence and presence of calmodulin.

Main Results:

  • Calmodulin-free Ca2+-pumping ATPase activity was over 40% lower in kwashiorkor membranes compared to normal.
  • Calmodulin significantly increased the maximum velocity of ATPase in normal membranes (4-fold) but had a lesser effect on kwashiorkor membranes (1.5-2 fold increase).
  • Kwashiorkor membranes showed lower affinity for ATP (Km 30.6 µM vs 21.7 µM), lower calmodulin affinity, and at least 70% lower Ca2+ affinity compared to normal membranes.

Conclusions:

  • The Ca2+-pumping ATPase enzyme in erythrocyte membranes of children with kwashiorkor is less functional.
  • Impaired calmodulin modulation and reduced affinity for ATP and Ca2+ contribute to the decreased activity of the calcium pump in kwashiorkor.
  • These findings suggest a potential disruption in cellular calcium regulation associated with kwashiorkor.

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