Submitted on October 24, 2002
Accepted on February 21, 2003
Measurement of Protein Metabolism in Epidermis and Dermis
Xiao-jun Zhang1, David L. Chinkes1, and Robert R. Wolfe2*
1 Metabolism Unit, Shriners Hospitals for Children, Galveston, Texas, USA; Department of Surgery, The University of Texas Medical Branch, Galveston, Texas, USA
2 Metabolism Unit, Shriners Hospitals for Children, Galveston, Texas, USA; Department of Surgery, The University of Texas Medical Branch, Galveston, Texas, USA; Department of Anesthesiology, The University of Texas Medical Branch, Galveston, Texas, USA
* To whom correspondence should be addressed. E-mail: rwolfe{at}utmb.edu.
We found that in the rabbit ear the dermal protein contains 75.5% of cutaneous phenylalanine and 97.9% of cutaneous proline; the remaining 24.5% of phenylalanine and 2.1% of proline are in the epidermal protein. This finding led us to develop two novel models which use phenylalanine and proline tracers and the rabbit ear to quantify protein kinetics in the epidermis and dermis. The 4-pool model calculates the absolute rates of protein kinetics and amino acid transport, and the 2-pool model calculates the apparent rates of protein kinetics that are reflected in the blood. The results showed that both epidermis and dermis maintained their protein mass in the postabsorptive state. The rate of epidermal protein synthesis was 93.4 ± 37.6 mg.100 g-1.h-1, which was 10 fold greater than that of the dermal protein (9.3 ± 5.8 mg.100 g-1.h-1). These synthetic rates were in agreement with those measured simultaneously by the tracer incorporation method. Comparison of the 4-pool and 2-pool models indicated that intracellular cycling of amino acids accounted for 75% and 90% of protein kinetics in the dermis and epidermis, respectively. We conclude that in the skin efficient reutilization of amino acids from proteolysis for synthesis enables the maintenance of protein mass in the postabsorptive state.
