Abstract
The quinonoid dihydropterin reductase (DHPR) activity and tetrahydropterin content were determined in human ciliary body-iris, retina, normal lens and senile cataracts. The DHPR activity was higher in the retina [120·56±12·46 nmol NADH oxidized min −1 (mg soluble protein) −1] than in the ciliary body-iris [46·10±7·46 nmol NADH oxidized min −1 (mg soluble protein) −1] and lens [2·79±0·15 nmol NADH oxidized min −1 (mg soluble protein) −1]. In the distribution of DHPR activity in the lens, the capsule-epithelium showed 1·5 and 10 times more activity than the cortex and nucleus, respectively. The apparent K m values for each of the substrates of DHPR activity in lens were obtained by Lineweaver-Burke plots. The tetrahydropterin content was found to be higher in the retina [826±76 pmol (g protein) −1] than in the ciliary body-iris [584±48 pmol (g protein) −1] and lens [82±16 pmol (g protein) −1]. The DHPR activity and tetrahydropterin content were decreased significantly in senile cataracts as compared with the values of age-matched clear lenses. The importance of the DHPR activity in the maintenance of tetrahydropterin in its reduced form in ocular tissues is discussed.
Published Version
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