Molecular aspects of the regulation of rat kidney alkaline phosphatase

[In vitro effects of 1,25-dihydroxycholecalciferol on alkaline phosphatase and gamma-glutamyltransferase activity in hypophysectomized rats]

Effects in vitro of 1,25-dihydroxycholecalciferol (1,25-(OH)2D3) on alkaline phosphatase (PAL), gamma-glutamyltransferase (gamma-GT) and acid phosphatase (PAC) activities were investigated on renal cortex from hypophysectomized rats. In these animals the biosynthesis of 1,25-(OH)2D3 and the specific activities of kidney PAL and gamma-GT were decreased. The course of these effects was determined from 45 min to 8 h. In the presence of 1,25-(OH)2D3 (2 x 10(-6) M) a delayed (5h) but simultaneous stimulation of the three enzymes was observed. It reached a maximum at 6h and disappeared at 8h. The dose-response relation was studied at 6h. In the presence of 1,25-(OH)2D3 (5 x 10(-7) M), the three enzymes were activated. The effect was maximal at 10(-6) M; it was +22% for PAL, +17% and +15% respectively for gamma-GT and PAC compared with controls. Cycloheximide suppressed the induction of PAL but not of gamma-GT activity. The effects of the secosteroid on renal enzymes seems to be a pharmacological more than a physiological one.

Increases of serum phosphorus concentration and duodenal, renal and femur alkaline phosphatase (EC 3.1.3.1) activities of normal rats fed 2000 ppm aluminum diets

In order to investigate the dietary effect of calcium on aluminum-induced hypophosphatemia, five types of diet, sucrose, lactose, milk, casein and soy protein, were prepared. These diets differed with regard to Ca concentration, and carbohydrate or protein sources which were expected to modify intestinal Ca absorption. Weanling Wistar rats were fed these diets for 67 days with the addition of Al at a concentration of 2000 ppm. Nutritional constituents had little effect on Al accumulation in the duodenum and bone. Al treatments had no effects on increases of body weight. The Al treatments significantly increased duodenum alkaline phosphatase (ALPase) activity and serum phosphorus concentration in all of the dietary groups. Slight but significant decreases of bone weight were observed. There were no significant increases in serum Al concentration but bone and kidney ALPase activities were also observed. These results suggest that Al ingestion can cause hyperphosphatemia in the intact animal. Effects of Al on nutrition should be considered even if serum Al concentration does not increase.

Effect of n-octane and n-nonane administration on alkaline phosphatase activity in tissues of female rats

Studies on alkaline phosphatase were conducted in albino rats exposed to n-octane or n-nonane for 2 and 7 days; there was an increase in alkaline phosphatase activity of liver, spleen and bone marrow. Increase in spleen alkaline phosphatase activity persisted up to 42 days after single dose of n-octane or n-nonane. Pretreatment with protein synthesis inhibitors, cycloheximide or ethionine removed this observed increase of alkaline phosphatase activity in liver and spleen.

Renal adaptation to a low phosphate diet in rats

The major renal adaptive changes in response to selective dietary phosphate restriction are a marked reduction in urinary excretion of phosphate and an increased urinary excretion of calcium; at the cellular level, there is selective increase in renal cortical brush border membrane phosphate uptake and increase in specific activity of alkaline phosphatase. In the present study we examined whether these functional and biochemical adaptive changes could be blocked by drugs known to inhibit protein synthesis. Administration of actinomycin D or cycloheximide to rats switched from a diet with normal phosphate content (0.7%) to a diet with low (0.07%) phosphate content either completely (actinomycin D) or partially (cycloheximide) prevented the expected decrease in urinary excretion of phosphate and increase in the urinary excretion of calcium. The specific activity of alkaline phosphatase measured in crude membrane fraction (washed 100,000 g pellet) from renal cortical homogenate in animals fed a low phosphate diet and treated with actinomycin D or with cycloheximide was significantly lower than in control animals also on a low phosphate diet receiving placebo; but there were no differences between treated and untreated animals in the activities of two other brush border enzymes, gamma-glutamyltransferase and leucine aminopeptidase. Actinomycin D administered to rats maintained on a normal phosphate diet throughout the course of the experiment caused an increase in the urinary excretion of phosphate on the last (6th) day of the experiment but did not change urinary excretion of calcium. In acute clearance experiments, infusion of actinomycin D to rats adapted to a low phosphate diet did not increase fractional excretion of phosphate. In separate experiments, using the same dietary protocol as above, brush border membrane fraction (vesicles) was prepared from renal cortex of rats sacrificed at the end of the experiment. In this preparation Na(+)-dependent (32)Pi and d-[(3)H]glucose uptake and activities of brush border enzymes membrane were determined. Brush border membrane vesicles prepared from rats fed a low phosphate diet showed significantly higher Na(+)-dependent (32)Pi uptake compared with rats fed a normal phosphate diet. This increase in (32)Pi uptake was completely prevented when rats on a low phosphate diet were simultaneously treated with actinomycin D. These differences were specific for (32)Pi transport as no differences were observed in d-[(3)H]glucose uptake among the three groups. There was a positive correlation (r = 0.82, P < 0.01) between (32)Pi uptake and specific activity of alkaline phosphatase measured in aliquots of the same brush border membranes, whereas no such correlation was observed with two other brush border membrane enzymes gamma-glutamyltransferase and leucine aminopeptidase. These observations show that actinomycin D prevents both the functional and cellular renal adaptive changes induced by a low phosphate diet. Taken together, these observations suggest that renal adaptation to a low phosphate diet could be prevented by inhibition of de novo protein synthesis.

Purification and properties of the trimethylamine dehydrogenase of bacterium 4B6

1. The trimethylamine dehydrogenase of bacterium 4B6 was purified to homogeneity as judged by analytical polyacrylamide-gel electrophoresis. The specific activity of the purified enzyme is 30-fold higher than that of crude sonic extracts. 2. The molecular weight of the enzyme is 161000. 3. The kinetic properties of the purified enzyme were studied by using an anaerobic spectrophotometric assay method allowing the determination of trimethylamine dehydrogenase activity at pH8.5, the optimum pH. The apparent K(m) for trimethylamine is 2.0+/-0.3mum and the apparent K(m) for the primary hydrogen acceptor, phenazine methosulphate, is 1.25mm. 4. Of 13 hydrogen acceptors tested, only Brilliant Cresyl Blue and Methylene Blue replace phenazine methosulphate. 5. A number of secondary and tertiary amines with N-methyl and/or N-ethyl groups are oxidized by the purified enzyme; primary amines and quaternary ammonium salts are not oxidized. Of the compounds that are oxidized by the purified enzyme, only trimethylamine and ethyldimethylamine support the growth of bacterium 4B6. 6. Trimethylamine dehydrogenase catalyses the anaerobic oxidative N-demethylation of trimethylamine with the formation of stoicheiometric amounts of dimethylamine and formaldehyde. Ethyldimethylamine is also oxidatively N-demethylated yielding ethylmethylamine and formaldehyde; diethylamine is oxidatively N-de-ethylated. 7. The activity of the purified enzyme is unaffected by chelating agents and carbonyl reagents, but is inhibited by some thiol-binding reagents and by Cu(2+), Co(2+), Ni(2+), Ag(+) and Hg(2+). Trimethylamine dehydrogenase activity is potently inhibited by trimethylsulphonium chloride, by tetramethylammonium chloride and other quaternary ammonium salts, and by monoamine oxidase inhibitors of the substituted hydrazine and the non-hydrazine types. 8. Inhibition by the substituted hydrazines is time-dependent, is prevented by the presence of trimethylamine or trimethylamine analogues and in some cases requires the presence of the hydrogen acceptor phenazine methosulphate. The inhibition was irreversible with the four substituted hydrazines that were tested.

Inhibition of monoamine oxidase by substituted hydrazines

1. The initial rate of inhibition of monoamine oxidase by phenethylhydrazine was shown to be similar, in pH-dependence and kinetic properties, to the oxidation of that compound by monoamine oxidase. 2. The time-course of irreversible inhibition of monoamine oxidase by phenethylhydrazine lags behind that of reversible inhibition. 3. Hydralzine was shown to be a reversible competitive inhibitor of monoamine oxidase, but phenylhydrazine is an irreversible inhibitor. Inhibition by the latter compound is not affected by the absence of oxygen, and the presence of substrate exerts no protective action. 4. Hydrazine does not inhibit monoamine oxidase unless a substrate and oxygen are present. 5. Phenethylidenehydrazine was found to be a time-dependent inhibitor of monoamine oxidase and the rate of inhibition was hindered by increasing oxygen concentration. 6. A mechanism for the inhibition of the enzyme by phenethylhydrazine is proposed in which the product of oxidation of this compound is a potent reversible inhibitor and an irreversible inhibitor of the enzyme. A computer simulation of such a mechanism predicts time-courses of inhibition that are in reasonable agreement with those observed experimentally.

The inducible alkaline phosphatase of rat heart. Some properties of the enzyme and factors influencing its activity

Subcutaneous injection of isoprenaline into rats produces a rapid rise in alkaline phosphatase activity which is largely confined to the right atrium of the heart. The phosphatase activity of extracts of atrial tissue from treated animals is on average four times that of controls. The rise in activity is largely suppressed by previously treating the animals with cycloheximide or actinomycin D. Comparison of the properties of the alkaline phosphatase in extracts of atria from isoprenaline-treated rats with control preparations shows the stimulated enzyme activity to be similar to that present in the resting state. In a number of respects, including substrate specificity, response to activators and inhibitors, rate of loss of activity on heating and electrophoretic mobility of the native and modified enzyme, the atrial phosphatase resembles alkaline phosphatases from other mammalian non-intestinal and non-placental tissues. These results suggest that the effect of isoprenaline is to increase the rate of synthesis of atrial alkaline phosphatase, and the ability of the tissues of the right atrium to respond in this way may be related to the rich sympathetic innervation of this part of the heart.