1 alpha-hydroxy-25-fluorovitamin D3: a potent analogue of 1 alpha,25-dihydroxyvitamin D3

Chemically synthesized 1 alpha-hydroxy-25-fluorovitamin D3 was compared to 1,25-dihydroxyvitamin D3 for potency in the chick intestinal cytosol-binding protein assay, induction of intestinal calcium transport, mobilization of calcium from bone, and epiphyseal plate calcification in the rat. The 25-fluorinated analogue causes 50% displacement of 1,25-dihydroxy[23,24-3H]D3 at 1.8 X 10(-8) M in the competitive protein-binding assay, whereas only 5.6 X 10(-11) M of unlabeled 1,25-dihydroxyvitamin D3 is needed for equal competition. This 315-fold difference between and 1 alpha-hydroxy-25-fluorovitamin D3 indicates that the fluoro analogue is about equipotent with 1 alpha-hydroxyvitamin D3 in the protein-binding assay. However, 1 alpha-hydroxy-25-fluorovitamin D3 is 1/50 as active as 1,25-dihydroxyvitamin D3 in vivo in the stimulation of intestinal calcium transport and bone calcium mobilization in vitamin D deficient rats on a low-calcium diet. Likewise, 1 alpha-hydroxy-25-fluorovitamin D3 is about 40 times less active than 1,25-dihydroxyvitamin D3 in inducing endochondrial calcification in rachitic rats. No selective actions of 1alpha-hydroxy-25-fluorovitamin D3 were noted. Since the 25 position of the analogue is blocked by a fluorine atom, it appears that 25-hydroxylation of 1 alpha-hydroxylated vitamin D compounds in vivo is not an obligatory requirement for appreciable vitamin D activity.     

The influence of dietary calcium and phosphorus on intestinal calcium transport in rats given vitamin D metabolites.

A new method for the simple analysis of methylated amino acids based on autoradiography is introduced. With this technique a survey of protein methylation in a prokaryote, Escherichia coli, and a eukaryote, fibroblasts in culture, was carried out in an attempt to identify, quantitate, and determine the subcellular localization of all the methylated amino acids found in the proteins of these organisms.In mammalian cells using an established mouse fibroblast line (3T3), we have found that nuclei-free and mitochondria-free cytoplasm contain readily detectable amounts of four identifiable methylated amino acids: N^?,N^?-dimethyllysine, N^?,N^?,N^?-trimethyllysine, N^G,N^G-dimethylarginine (or N^G-methylarginine), and N^G,N′^G-dimethylarginine. The crude nuclear pellet also contains these methylated amino acids, but in addition contains N^?-methyllysine and a new as yet unidentified methylated compound. Histones purified from these nuclei contain essentially the same array of methylated compounds.The ribosomal subunits of the mammalian cells contained only small amounts of the methylated amino acids; the 40S subunit contained a substantial amount of just one, N^G,N^G-dimethylarginine (or N^G-methylarginine), and smaller amounts of N^G,N′^G-dimethylarginine, and an as yet unidentified methylated compound. The 60S subunit contained even smaller amounts of methylated amino acids, 50% of which was N^?,N^?,N^?-trimethyllysine and smaller amounts of N^?-methyllysine, N^?,N^?-dimethyllysine, and N^G,N^G-dimethylarginine. These subunits also contained an as yet unidentified methylated compoundThese results were in marked contrast to those that we obtained with the prokaryote, Escherichia coli. Only the proteins of the 50S ribosomal subunit of the bacteria contained methylated amino acids. Of those present 50% was N^?,N^?,N^?-trimethyllysine, with the remainder distributed about equally between N^?-methyllysine and three unknowns, one of which is apparently the same as that found in the 60S subunit of the mouse fibroblasts. All of the N^?-methyllysine was apparently in the small acidic proteins, L7 and L12.     

The role of 1,25-dihydroxyvitamin D3 and parathyroid hormone in the regulation of chick renal 25-hydroxyvitamin D3-24-hydroxylase.

A single 325-pmol dose of 1,25-dihydroxyvitamin D₃ given to chicks fed a vitamin D-deficient diet containing 3% calcium and 0.6% phosphorus suppresses renal mitochondrial 25-hydroxyvitamin D₃-1α-hydroxylase and stimulates the 25-hydroxyvitamin D₃-24-hydroxylase as measured by in vitro assay. This alteration in the enzymatic activity takes place over a period of hours. The administration of parathyroid hormone rapidly suppresses the 25-hydroxyvitamin D₃-24-hydroxylase. The alterations in the hydroxylases by parathyroid hormone or 1,25-dihydroxyvitamin D₃ are not related to changes in serum clacium or phosphate but could be related to changes in intracellular levels of these ions. Actinomycin D or cycloheximide given in vivo reduces the 25-hydroxyvitamin D₃-24-hydroxylase activity rapidly which suggests that the turnover of the enzyme and its messenger RNA is rapid (1- and 5-h half-life, respectively). The half-lives of the hydroxylases are sufficiently short to permit a consideration that the regulation by 1,25-dihydroxyvitamin D₃ and parathyroid hormone may involve enzyme synthesis and degradation.     

An in vitro study of vitamin D2 hydroxylases in the chick.

An in vitro study of the liver 25-hydroxylation of vitamin D2 and the kidney 1- and 24-hydroxylations of 25-hydroxyvitamin D2 was undertaken in order to determine whether the discrimination against vitamin D2 seen in chicks in vivo is the result of a block of one or more of the steps in the activation of the vitamin D2 molecule. Vitamin D2 hydroxylation reactions in the chick are virtually identical with those observed with the vitamin D3 series. It is, therefore, concluded that the chick possesses the required enzymatic machinery to synthesize 1,25-dihydroxyvitamin D2 and that the discrimination must be because of some unknown metabolic reaction of the vitamin D2 compounds, to a defect in the transport of vitamin D2 metabolites, or to target organ discrimination.     

Multiple forms of vitamin D-dependent calcium-binding protein in rat kidney

The technique of two-dimensional electrophoresis was used in combination with a highly sensitive silver stain to study vitamin D-dependent calcium-binding protein (CaBP) in rat kidney. Rat renal CaBP was shown to co-migrate almost exactly with CaBP purified from chick intestine suggesting evolutionary conservation of this protein. In some cases rat renal CaBP appeared not as a single polypeptide, but rather as a cluster of 4 polypeptides. Formation of the satellite cluster of CaBP in response to high doses of 1,25-dihydroxyvitamin D3 occurred in young rats which had been maintained on a vitamin D-deficient diet for 2 weeks, as well as in older rats which had been maintained on the same diet for 5 months. The 4 forms of CaBP were not the result of various states of Ca2+ binding, but rather the result of an enzymatic reaction. This was shown by 3 experiments. 1) Adding excess EGTA to samples containing the 4 satellite forms did not change the two-dimensional electrophoretogram. 2) Incubation of purified chick intestinal CaBP with kidney cytosols from D-deficient rats brought about the formation of the satellite CaBP forms from the chick protein. However, purified chick CaBP was unchanged by incubation in buffer alone for up to 2 h at 37 degrees C. 3) Placing rat kidney cytosols in a boiling water bath for 10 min inactivated the factor which generated the satellite forms as would be expected for an enzyme. The physiological significance of these forms of CaBP is as yet unknown.     

Turnover and trends in butterfly communities on two British tidal islands: stochastic influences and deterministic factors

Aim Community trends were investigated for two small islands and two local mainland butterfly communities within the UK over a period of 20–30 years. Location Hilbre Island off the Wirral Peninsula at 53.33° N, 3.10° W; Lindisfarne, an island off the Northumberland coast at 56.41° N, 1.48° W; Leighton Moss at 54.08° N, 2.26° W; Wyre Forest at 52.23° N, 2.14° W, UK. Methods Butterfly species data were collected on Hilbre and two mainland sites (Leighton Moss and Wyre Forest) from 1983 to 2006, and on Lindisfarne from 1977 to 2006, as part of the National Habitat Survey, the UK Butterfly Monitoring Scheme and ‘Butterflies for the New Millennium Atlas’ recording. Matrices of associations (Sokal and Michener’s matching coefficient S_SM; resemblance coefficient) were computed between years and subject to non‐metric multidimensional scaling (NMDS) and Mantel tests. The pattern of extinctions and colonizations at sites were examined, their heterogeneity tested by applying a Friedman test to fractional incidences for the same years. Regression analysis (multiple regression and logit regression) was used to relate butterfly numbers and incidences to climate variables, time and previous records. Results Significant community trends based on population counts and species’ incidences were found for all four sites. There was a significant climatic signal for Hilbre; although this was not apparent for the remaining sites, significant associations occurred between records for a number of species and climatic variables at all sites. Substantial turnover of species on the islands was inversely related to numbers of records for species but not to their conspicuousness to recorders. Main conclusions We argue that time trends are widespread in butterfly communities, even for relatively short periods; they are largely generated by stochastic influences rather than by more substantive factors such as climate change. Potential biases in surveying and recording history are shown to be unlikely. A clear climate signal was found only for the small Hilbre Island, for which there was also evidence for the significant influence of colonization capability of individual source species. We conclude that for many species, small islands will be sinks or pseudosinks and their ‘populations’ vulnerable to small changes in source–sink dynamics.