The activities of γglutamylcysteine synthetase and glutathione synthetase, the two enzymes required for glutathione synthesis, were determined as a function of age in lenses of three species of Old World higher primates: orangutan, pigtail monkey and olive baboon. These we're compared to enzyme activities in lenses of two prosimians: mouse lemur and galago. γGlutamylcysteine synthetase activity decreased as a function of age in all three Old World simians. The rate of decrease was greatest in the juvenile lenses. In contrast, the enzyme activity increased continuously with age in the galago lens. In the mouse lemur the enzyme activity increased per lens, but was constant when expressed as specific activity or as units per gram of lens. The loss of enzyme activity with age was limited to Old World higher primates apparently representing genetic change. Glutathione synthetase activity decreased logarithmically with age in the lenses of all five species.
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ACKNOWLEDGMENTS The authors wish to thank Alice Schmidt for technical aid and the personnel at the following institutions for supplying lenses: Delta Regional Primate Research Center, Duke University Primate Research Center, University of Oregon Regional Primate Research Center, University of Washington Regional Primate Research Center, Yerkes Regional Primate Research Center, the Southwest Foundation for Biomedical Research, the St. Louis Zoo and the Como Park Zoo of St. Paul, Minnesota. This research was supported in part by the National Institutes of Health research grant EY-01197 and an unrestricted grant from Research to Prevent Blindness, Inc.