. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. LENS DIFFERENTIATION 207. LAYER FIGURE 16. Changes in both water-soluble and water-insoluble protein content in concentric layers of the squirrel lens. TSP = water-insoluble; US = urea-soluble; SDS = sodium dodecyl sulphate-soluble; SDS + DTT = SDS plus dithiothreitol soluble proteins. Positional differences are seen not only with regard to structural proteins, but they also apply to many enzymes of great importance to cell function (see Hockwin and Ohrloff, 1981). For example, the ATPase activity is greatest in the outer la
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. LENS DIFFERENTIATION 207. LAYER FIGURE 16. Changes in both water-soluble and water-insoluble protein content in concentric layers of the squirrel lens. TSP = water-insoluble; US = urea-soluble; SDS = sodium dodecyl sulphate-soluble; SDS + DTT = SDS plus dithiothreitol soluble proteins. Positional differences are seen not only with regard to structural proteins, but they also apply to many enzymes of great importance to cell function (see Hockwin and Ohrloff, 1981). For example, the ATPase activity is greatest in the outer layers of the lens, and tend to diminish toward the nucleus (see Table II). With regard to the Na+/K+ enzyme, diminished activity in the nucleus leads to light-scattering stimulation due to disturbances in the salt and water balance in this region. Positional differences between outer less mature and inner more mature regions of the lens apply to several other features of the lens. In one case, there are stable free radicals in the lens whose concentration diminishes toward the nucleus (Fig. 20). It has been hypothesized that the chemical entities that represnt the free radicals are bound to proteins and in fact serve as cross-linking agents. Due to the conservative nature of the lens, such cross-linking agents react with proteins that are finally found in the nucleus, and therefore become quenched with regard to free radical properties (Zigman, 1981). Another lens component that changes in properties and levels from the outer to inner portions of the lens is the yellow pigment that is present nearly exclusively in diurnally active animals, such as squirrels, monkeys, and humans. The pigments that are present in the lens at birth both in humans and in squirrels, are water- soluble, low molecular weight entities (see Fig. 21). Tentatively speaking, the human pigment is 3-OH kynurenine-glucoside (Bando, 1983; Van Heyningen, 1973), while the squirrel pigment is thought to be n-acety
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
