A comparative study of the in vitro activities of three enzymes - Na⁺,K⁺ adenosine triphosphatase, γ -glutamyl transpeptidase, and ornithine decarboxylase - in skin sampled from Merino sheep with different capacities for wool growth

Abstract

The concentration of sodium, potassium adenosine triphosphatase, and the in vitro activities of p-glutamyl transpeptidase and ornithine decarboxylase, were studied in skin from Merino sheep to determine whether these traits differed in skin from sheep whose rate of wool production was influenced by genetic and dietary factors. Sheep from 2 flocks were compared, these being selectively bred for high (Fl+') or low (Fl-') clean fleece weight per head. The sheep were given one of 2 pelleted rations (L and H). The L ration provided metabolisable energy approximately equal to 0.75 times maintenance. The H ration provided approximately twice maintenance, and this ration had a higher protein content due to the inclusion of formaldehyde-protected casein. Eight sheep were studied in each flock at each dietary level. The average concentration of sodium, potassium adenosine triphosphatase, measured by 3H ouabain binding, was 132 pmol/g air-dry skin (s.e.d. = ¦ 30). The activity of p-glutamyl transpeptidase was 0.698mol product/h.mg protein from skin (s.e.d. = ¦ 0.17). The average activity of ornithine decarboxylase in skin was 6.0 8mol carbon dioxide released/h.g skin (s.e.d. ¦ 1.2). Plucking of fibres from the skin 4 h before sampling resulted in an increase (P < 0.05) in the activity of ornithine decarboxylase to 12.9 nmol carbon dioxide1h.g skin. For each of the enzymes, the measured values tended to be greater in the skin of sheep from the genetically high-producing flock and in skin from sheep on the H ration, but none of these differences was statistically significant.