The microsomal Na+-K+-ATPase of rat brain was inhibited by mercury chloride and methyl mercury. The IC50 was 6.5 X 10(-7) M for mercury chloride and 3.5 X 10(-6) M for methyl mercury. The inhibition was of a non-competitive type with respect to ATP. The non-ionic detergent Lubrol potentiated the inhibitory effect of both mercurials. It is concluded that Lubrol removes the bulk lipids present outside the catalytic center of the enzyme. Consequently, the enzyme will become more sensitive to the inhibition by both mercurials.
Myelin isolated from the central nervous system of Xenopus tadpoles was characterized biochemically and compared with Xenopus frog and mammalian myelins. Xcnopi4.s tadpole myelin contains the characteristic protein and lipid components of mammalian myelin, although quantitative differences exist. The biochemical composition of Xenopirs tadpole myelin suggests that it is an immature form of XPnopus frog myelin. Basic protein and proteolipid protein are prominent components of Xenopus myelin, but isolated tadpole myelin contains a greater proportion of higher molecular weight proteins than Xenopirs frog or mature mammalian myelin. The basic protein has a higher apparent molecular weight than mammalian myelin basic protein. The levels of 2',3'-cyclic nucleotide 3'-phosphodiesterase are significantly higher in whole tadpole brain homogenate and purified myelin than in similar mammalian preparations. Tadpole myelin lipids contain a higher proportion of phospholipids and less galactolipid than mammalian myelin. Tadpole myelin galactolipids include a high (16%) percentage of monogalactosyl diglyceride, a component found in only trace quantities (0.9%) in bovine myelin.
Mouse brain synaptosomal Na +/K + ‐ATPase was inhibited by 23%, 18 hrs after a single intraperitoneal dose of 40 mg lindane (dissolved in olive oil) per kg. The inhibition was of a non‐competitive type with respect to ATP. Pretreatment with lindane also potentiated the inhibitory effect of ethanol on this enzyme. It is suggested to consider this interaction at the synaptosomal level when evaluating the anaesthetic effect of ethanol in contaminated persons. Although the synaptosomal Na +/K + ‐ATPase was inhibited after pretreatment with lindane in vivo, neither lindane nor its metabolites were present in the synaptosomal fraction when determining the subcellular distribution of U‐[14C]‐lindane in the brain. These results raise some questions regarding the current opinion that lindane exerts some of its central effects through binding to the synaptosomal membrane.
The effect of manganese on free polysomal protein synthesis of immature rat brain (3 weeks old) has been determined after 1, 2, 3, and 4 weeks of daily intake of 55 pg manganese/ml of drinking water. The protein synthesis was inhibited up to 35% during the first 3 weeks and returned toward the control levelduring the fourth week of treatment. Cross-incubation experiments with polysomes and p H 5 enzyme fractions indicated that the inhibition of protein synthesis is due to alteration of the pH 5 enzyme fraction. Furthermore, cerebral t-RNA content was reduced by 20% during the first 3 weeks and also returned to the control level after 4 weeks. The data suggest that the previously reported retardation in learning and memory of manganese treated immature rats may partly be due to alteration of cerebral RNA and protein synthesis. It was also evident that an adaptation mechanism to the observed effect of manganese developes after three weeks of daily intake of 55 pg manganese/mI.
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