Alkaline phosphatase

About: Alkaline phosphatase is a research topic. Over the lifetime, 20218 publications have been published within this topic receiving 540547 citations. The topic is also known as: Alkaline_phosphatase & IPR001952.

Characteristics of phosphorus deficiency in anabaena1

Abstract: SUMMARY Several aspects of the metabolism and composition of a strain of Anabaena have been studied during phosphorus deficiency. The effects of medium composition, substrate concentration, temperature, pH, and illumination on alkaline phosphatase activity and phosphate uptake have been examined. Of particular interest among these results was the dependence of maximum alkaline phosphatase activity on Ca and of phosphate uptake on Mg. Depletion of dissolved phosphate from the culture medium runs accompanied by a marked increase in alkaline phosphatase activity, initial rate of phosphate uptake, and total amount of phosphate taken up to satisfaction of the phosphorus debt. Readdition of phosphate to a phosphorus-deficient culture resulted in a rapid decline in the ability to take up phosphate but no loss of alkaline phosphatase beyond dilution of activity already present. Entry into phophorus deficiency was accompanied by a loss of heterocysts, a decline in chlorophyll a, protein, RNA, and cellular phosphorus, and an increase in carbohydrate per unit dry weight. The possible use of these changes as physiological indicators of phosphorus limitation in natural situations is discussed.

Mice deficient in Abl are osteoporotic and have defects in osteoblast maturation.

Abstract: The c-Abl protein is a non-receptor tyrosine kinase involved in many aspects of mammalian development. c-Abl kinase is widely expressed, but high levels are found in hyaline cartilage in the adult, bone tissue in newborn mice, and osteoblasts and associated neovasculature at sites of endochondrial ossification in the fetus1,2. Mice homozygous for mutations in the gene encoding c-Abl (Abl) display increased perinatal mortality, reduced fertility, foreshortened crania and defects in the maturation of B cells in bone marrow3,4. Here we demonstrate that Abl−/− mice are also osteoporotic. The long bones of mutant mice contain thinner cortical bone and reduced trabecular bone volume. The osteoporotic phenotype is not due to accelerated bone turnover—both the number and activity of osteoclasts are similar to those of control littermates—but rather to dysfunctional osteoblasts. In addition, the rate of mineral apposition in the mutant animals is reduced. Osteoblasts from both stromal and calvarial explants showed delayed maturation in vitro as measured by expression of alkaline phosphatase (ALP), induction of mRNA encoding osteocalcin and mineral deposition.

Alteration of the amino terminus of the mature sequence of a periplasmic protein can severely affect protein export in Escherichia coli

Abstract: Escherichia coli alkaline phosphatase, coded for by the phoA gene, is normally translocated across the cytoplasmic membrane into the periplasm with high efficiency. We have constructed a series of derivatives of the phoA gene that code for a wild-type signal sequence but result in altered amino acid sequences at the amino terminus of the mature alkaline phosphatase. Our results suggest that the presence of two positively charged amino acids very early in the mature sequence interferes significantly with protein export. In one case, phoA2AB, the presence of the sequence Arg-Ile-Arg at the amino terminus of alkaline phosphatase results in a 50-times reduction in the export of the protein. By using oligonucleotide-directed mutagenesis, we have constructed mutant derivatives of phoA2AB that are greatly enhanced for export. In all cases, these derivatives reduce the net positive charge in the region. Our results may explain the failure of E. coli to export a number of proteins coded for by artificial constructs and suggest a way to improve export in these cases.