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The Journal of biological chemistry1987; 262(23); 11140-11148;

The concentrations of free Mg2+ and free Zn2+ in equine blood plasma.

Abstract: The enzyme phosphoglucomutase can be used as a metal ion indicator to measure the concentrations of free Mg2+ and free Zn2+ in physiological fluids. In horse plasma, the concentration of free Mg2+ is close to 0.5 mM, whereas that of free Zn2+ is about 2 X 10(-10) M, although numerous physiological roles for Zn2+ have been postulated that would require free Zn2+ concentration orders of magnitude higher than this. A titration of plasma with Zn2+ shows that the fractional increase in free Zn2+ is essentially the same as the fractional increase in total exchangeable Zn2+, and the results are consistent with a model in which essentially all of the Zn2+ in plasma is bound to albumin. Regardless of the model, the buffering capacity of plasma for free Zn2+ is intrinsically low; however, its capacity relative to the total (exchangeable) Zn2+ present is maximal. The implications of this type of buffering for homeostasis of plasma Zn2+ are considered. Treatment of plasma with a strong reducing agent such as dithiothreitol (0.1 mM) substantially increases the apparent binding of Zn2+ and thus reduces the free Zn2+ concentration. However, the concentration of free Zn2+ appears to be insensitive to decreases in the physiological concentrations of reduced glutathione and cysteine. The concentrations of free Zn2+ and free Mg2+ in plasma are similar to those that have been reported for muscle tissue (rabbit). Their ratio is about 4 X 10(-7). The physiological implications of these concentrations are considered. In some cases, if the Zn2+ and Mg2+ complexes of an uncharacterized vertebrate protein exhibit significantly different properties, their relative importance under physiological conditions can be approximated by evaluating those of the mixed complexes present in a solution that contains the physiological concentration of free Mg2+, plus Zn2+ buffered with histidine, at the appropriate pH and ionic strength. Other metal ion/chelon systems that come close to reproducing the concentrations of free Mg2+ and free Zn2+ in horse plasma also are considered.
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Publication Date: 1987-08-15 PubMed ID: 2956262
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  • Journal Article
  • Research Support
  • U.S. Gov't
  • P.H.S.

Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

This study investigates the concentrations of two types of metal ion, namely free Mg2+ and free Zn2+, in horse blood plasma, using the enzyme phosphoglucomutase as a marker. The study also examines the role of various factors, such as the reducing agent dithiothreitol and proteins in plasma, in managing these concentrations and their physiological significance.

Measuring Free Mg2+ and Zn2+ Concentrations

  • This research conducted measurements of free Mg2+ and free Zn2+ concentrations in horse plasma using the enzyme phosphoglucomutase as an indicator.
  • Results revealed that the concentration of free Mg2+ was approximately 0.5 mM, whereas the free Zn2+ concentration came at about 2 X 10(-10) M, which is significantly lower than what its predicted physiological roles would require.

Zn2+ Binding and Plasma Buffering Capacity

  • When titration of plasma with Zn2+ was carried out, the research found that the fractional increase in free Zn2+ paralleled the fractional increase in total exchangeable Zn2+, suggesting that the bulk of Zn2+ in plasma is possibly tied to albumin, a protein in the blood.
  • While the buffering capacity of blood plasma for free Zn2+ is inherently low, its capacity concerning the total zinc present is found to be maximal.

Effects of Reducing Agents and Proteins

  • The study further showed that treatment of plasma with a strong reducing agent (dithiothreitol at 0.1 mM) prompted a significant upsurge in the apparent binding of Zn2+, thereby shrinking free Zn2+ concentration.
  • Additionally, the concentration of free Zn2+ seemed immune to drops in physiological concentrations of reduced glutathione and cysteine, two important amino acids.

Comparison with Muscle Tissue and Physiological Implications

  • The research indicates that the concentrations of free Mg2+ and free Zn2+ in horse plasma bear resemblance to those reported for rabbit muscle tissue.
  • It’s also noted that the ratio of these two ions is about 4 X 10(-7).
  • The study finally explores the physiological implications of these concentrations. It highlights the notion that in some cases, differences in properties of Zn2+ and Mg2+ complexes in a vertebrate protein may inform their importance under physiological conditions.

Cite This Article

APA
Magneson GR, Puvathingal JM, Ray WJ. (1987). The concentrations of free Mg2+ and free Zn2+ in equine blood plasma. J Biol Chem, 262(23), 11140-11148.

Publication

The Journal of biological chemistry
ISSN: 0021-9258
NlmUniqueID: 2985121R
Country: United States
Language: English
Volume: 262
Issue: 23
Pages: 11140-11148

Researcher Affiliations

Magneson, G R
    Puvathingal, J M
      Ray, W J

        MeSH Terms

        • Animals
        • Binding, Competitive
        • Cations, Divalent
        • Dithiothreitol / pharmacology
        • Horses / blood
        • Hydrogen-Ion Concentration
        • Magnesium / blood
        • Muscles / enzymology
        • Phosphoglucomutase / metabolism
        • Plasma / analysis
        • Protein Binding
        • Serum Albumin / metabolism
        • Spectrophotometry, Atomic
        • Zinc / blood

        Grant Funding

        • 08963 / PHS HHS

        Citations

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