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Modulation of Lysyl Oxidase by Dietary Copper in Rats^1,2,

Robert B. Rucker^*,3, Nadia Romero-Chapman^*, Toniel Wong^*, Jill Lee^*, Francene M. Steinberg^*, Carl Mcgee^*, Michael S. Clegg^*, Karen Reiser, Taru Kosonen^*, Janet Y. Uriu-Hare^*, Jerome Murphy^** and Carl L. Keen^*

^* Departments of Nutrition (College of Agriculture and Environmental Sciences) Pulmonary Medicine ^** Pediatrics (School of Medicine), University of California, Davis, CA 95616

Lysyl oxidase levels were estimated in rat tissues using an enzyme-linked immunosorption assay (ELISA) and a functional assay standardized against known amounts of purified lysyl oxidase. High concentrations of lysyl oxidase (150 µg/g of tissue or packed cells) were detected in connective tissues, such as tendon and skin. Values for aorta, kidney, lung and liver ranged from 30 to 150 µg/g of tissue; values for skeletal muscle and diaphragm were <30 µg/g tissue. Purified rat skin lysyl oxidase catalyzed the release of 50–100 Bq of tritium per µg enzyme in assays that used ³H-elastin-rich substrates. In dense connective tissues, good agreement was obtained for the values from ELISA and those derived from measurements of functional activity in aorta, lung, skin and tendon (r² > 0.9). When egg white-based experimental diets containing 2 or 10 µg/g added copper were fed to weanling rats, values for skin lysyl oxidase functional activity in the group fed 2 µg/g added copper were one-third to one-half the values for skin lysyl oxidase functional activity in rats fed 10 µg/g copper. This reduction in lysyl oxidase activity, however, had minimal effect on indices of collagen maturation in rat skin, e.g., collagen solubility in neutral salt and dilute acid or the levels of acid stable cross-links. Moreover, copper deficiency did not influence the steady-state levels of lysyl oxidase specific mRNA in rat skin or the apparent amounts of lysyl oxidase in rat skin as determined by ELISA. These observations underscore that the concentration of lysyl oxidase is relatively high in dense corrective tissues, and although decreasing dietary copper influences functional activity, there is little apparent effect on the production of lysyl oxidase protein.

KEY WORDS: • copper • lysyl oxidase • collagen • elastin • rats

¹ Supported in part by National Institutes of Health grants HL-15956, AG-05324, AM-25358 and HD-26777 (RBR, KR, JU-H, CK), Cooperative Agreement from the U.S. Department of Agriculture (92-37200-4429) (RBR), funds from the Cigarette and Tobacco Surtax Fund (State of California) through the Tobacco-Related Disease Research Program of the University of California (RBR), and a predoctoral fellowship from The Academy of Finland (TK). CM received funding from the Medical Research Council of Canada.

² The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

³ To whom correspondence should be addressed.

Manuscript received 23 January 1995. Revision accepted 22 August 1995.