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Dietary Copper Deficiency Alters Protein and Lipid Composition of Murine Lymphocyte Plasma Membranes¹

Departments of Biochemistry and Chemistry, University of Minnesota, Duluth, MN 55812

Protein and lipid analyses were conducted on isolated erythrocyte and lymphocyte plasma membranes from 7-wk-old male C57BL copper-deficient and copper-supplemented mice to investigate mechanisms for the altered immunity that accompanies dietary copper deficiency. Beginning at parturition, dams were fed a diet low in copper (0.5 mg/kg) and the offspring were weaned to this diet. Half the dams and their respective offspring received supplemental copper (20 mg/L) in the drinking water (+ Cu) and served as controls. Unsupplemented offspring (- Cu) had lower activity of cuproenzymes serum ceruloplasmin, spleen and thymus cytochrome-c oxidase and copper,zinc-superoxide dismutase. The - Cu mice exhibited anemia, splenomegaly and thymic atrophy. Based on the marker enzyme alkaline phosphodiesterase 1 (APDE-I), lymphocyte plasma membranes were enriched 7- to 10-fold for spleen and thymus, respectively, after discontinuous sucrose density centrifugation. The activity of APDE-I was higher in spleen and thymus samples from - Cu mice than from those of + Cu mice for both crude homogenates and purified plasma membranes. Proteins were fractionated by sodium dodecyl sulfate—polyacrylamide gel electrophoresis followed by silver staining. A yellow-appearing band, M_r 74,000, present in all spienic membrane samples from + Cu mice was not evident in the samples from - Cu mice. Fatty acid methyl esters (FAME) were quantified by gas chromatography. Compared to splenic membranes from + Cu mice, the samples from - Cu mice demonstrated significant changes in all FAME (lower 16:0, 18:0 and 20:3n-6 and higher 18:1n-9, 18:2n-6 and 20:4n-6), including a higher unsaturation index. FAME composition of erythrocyte ghosts from - Cu mice demonstrated similar changes. The protein and FAME composition of thymus plasma membranes was similar for both groups of mice. The compositional changes observed in - Cu mice, especially for splenocytes, may influence membrane fluidity and the immune response.

KEY WORDS: • copper-deficient mice • lymphoctyes • plasma membranes • protein composition • fatty acid composition

¹ This research was supported in part by Grant Nos. HD-15491, HD-20975 and BRSG S07 RR-058986 from the National Institutes of Health.

Manuscript received 18 August 1986. Revision accepted 12 February 1987.