Measurement of free magnesium and free zinc in blood plasma by enzymic assay

Conference · Fri May 01 00:00:00 EDT 1987 · Fed. Proc., Fed. Am. Soc. Exp. Biol.; (United States)

OSTI ID:6175405

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

While the measurement of free Mg in biological fluids is accessible by different means, a methodology for measuring physiological levels of free Zn has not been previously reported. The authors have developed an accurate in vitro assay system for free Mg and free Zn in biological fluids which employs an exogenous enzyme, muscle phosphoglucomutase (PGM), as a metal ion indicator. PGM is maximally activated by Mg and is inhibited competitively by Zn. Free Mg values were determined from plasma supplemented with the dephospho form of PGM by using a burst of product assay. Enzymic activity is a function of the fractional saturation of PGM with Mg. Interference from Zn binding was eliminated by adding lyophilized histidine to plasma. The assay for free Zn involved the equilibration of the phospho form of PGM with sample for which free Mg was known and subsequent assessment of the degree of Zn inhibition by initial velocity assay. Free Zn values were calculated from the molar ratio of Zn and Mg forms of PGM, the free Mg concentration, and enzyme-metal stability constants. In equine plasma, the concentration of free Mg is close to 0.5 mM and free Zn is about 2 x 20/sup -10/ M. A titration of plasma with Zn indicates that nearly all of the exchangeable Zn is bound to albumin and the concentration of free Zn is essentially unbuffered. This enzymic assay system may be a useful tool for the evaluation of marginal Zn deficiency.

• Research Organization: Purdue Univ., West Lafayette, IN
• OSTI ID: 6175405
• Report Number(s): CONF-870644-
• Journal Information: Fed. Proc., Fed. Am. Soc. Exp. Biol.; (United States), Vol. 46:6; Conference: 78. annual meeting of the American Society of Biological Chemists conference, Philadelphia, PA, USA, 7 Jun 1987
• Country of Publication: United States
• Language: English

Related Subjects

63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.
HYDROLASES
ENZYME ACTIVITY
MAGNESIUM
BIOASSAY
METABOLISM
PHOSPHOTRANSFERASES
ZINC
BLOOD PLASMA
HISTIDINE
IN VITRO
NUTRITIONAL DEFICIENCY
ALKALINE EARTH METALS
AMINO ACIDS
AZOLES
BIOLOGICAL MATERIALS
BLOOD
BODY FLUIDS
CARBOXYLIC ACIDS
ELEMENTS
ENZYMES
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
IMIDAZOLES
MATERIALS
METALS
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PHOSPHORUS-GROUP TRANSFERASES
TRANSFERASES
560300* - Chemicals Metabolism & Toxicology