Substrate specificity of mammalian folylpoly-gamma-glutamate synthetase for 5,8-dideazafolates and 5,8-dideaza analogues of aminopterin

The substrate specificity of pig liver folylpolyglutamate synthetase (tetrahydrofolate:L-glutamate gamma-ligase (ADP-forming), EC 6.3.2.17) for classical 5,8-dideaza analogues of folic acid, isofolic acid aminopterin and isoaminopterin has been investigated. 5,8-Dideazafolate and 5,8-dideazaaminopterin are very effective substrates with activities approaching those of the best reduced folate substrates. The analogous isofolate analogues are less effective substrates, but still better than folic acid. The 5-chloro substituent is the only modification that consistently increases the on rate, with 5-chloro-5,8-dideazaaminopterin being the most effective substrate found, thus far, for the enzyme. Methylation at positions 9 or 10 generally decreases binding, while 5-methylation increases the binding of 4-oxoquinazolines, but decreases the binding of their 4-amino counterparts. The presence of a formyl group at N9 or N10 has the opposite effect, decreasing the binding of 4-oxo analogues while increasing the rate for 4-amino derivatives. Increases in on rate with methyl, formyl or 4-amino substitutions are only significant when the parent compound is a poor substrate, suggesting that these groups do not interact directly with the enzyme but cause conformational changes in the structure of the substrate that influence binding to the enzyme.     

Thyroxine and palatal development in rat embryos

The placental transport and palatal localization of l-thyroxine-¹²⁵I was studied in Sprague-Dawley rat embryos ages 13 and 14 days in vivo and 14–16 days in vitro. Amniotic fluid, placenta and (by late day 14) embryonic/palatal and liver areas were assayed by scintillation counting and protein analysis. Radioactivity was found in amniotic fluid as early as 13 days in vivo. A small but consistent amount of radioactivity above control levels was found in the embryonic palatal and liver areas. Autoradiographs of thin-layer chromatographs showed that most of the radioactive label was at the thyroxine area in both 13- and 14-day in vivo and 15-day in vitro amniotic fluid pools. A small amount of radioactivity was present in the diiodothyronine area in both. Some activity was also present in the triiodothyronine area in the 13- and 14-day samples. No labelled inorganic iodide was detectable. The thyroid gland in rat does not begin to function until 17 days in utero. Accordingly, the labelled thyroxine was exogenous. The presence of labelling in the embryonic palate suggests a possible involvement of this hormone in palatal embryogenesis.     

Rates of small-scale species mobility in alvar limestone grassland

Abstract. Small-scale species frequency and cumulative species frequency were studied in four plots in limestone grassland of the Veronica spicata-Avenula pratensis association on Stora Alvaret on the Baltic island of Öland, Sweden. Species mobility was expressed as increase in cumulative species frequency in 20 subplots of 100 cm². Observed cumulative frequencies from 1985–1989 in all four plots, and from 1985–1995 in one plot were compared with values following from two null models, a ‘minimal mobility’ model and a random mobility model. In ca. 50 % of the cases the observed cumulative frequency was not significantly different from the random expectation. However, in many such cases the mean annual frequency was either very high or very low. Three ways of calculating the mobility rate are presented though only one is used: (observed cumulative frequency -lowest annual frequency) / expected cumulative frequency. Values × 100 range from 0 to 100. There were slight differences between the four plots which were interpreted in terms of differences in grazing intensity and soil depth. It is stressed that the idea of the Carousel model has never been meant to suggest that all species would show random mobility, which we now quantify, but that species differ in their mobility rate and that the mean rate is much higher than generally realized.     

The innervation of some proboscis structures involved in feeding behavior of the blowfly (Calliphora vicina)

The microtopology of the motoneurons involved in protraction and retraction of the proboscis of the blowfly (Calliphora vicina) has been studied. In addition, taste input from the labellar hairs was investigated. As a result of this study it appears that protraction movements are controlled by two while retraction movements are guided by three motoneurons on each side. The neurons in each group apear to be in ipsicontralateral communication with each other. The musculi protractores fulcri (MPF) probably contain a proprioceptive cell group which projects to the MPF motoneurons. It is proposed that the proboscis motor system can be modulated by proprioception as well as by chemosensory labellar input. Neurosecretory cells may be involved in adjusting muscle power.     

Absence of functional and structural homology of natural and recombinant human leukocyte interferon (IFN-α) with human α-ACTH and β-endorphin

A comparison of the amino acid sequence of one human recombinant IFN-α (IFLrA) with either human β-endorphin or ACTH reveals only a minimal and insignificant degree of homology. Also, synthetic ACTH, β-endorphin and β-endorphin-(1–15) have no antiviral protective effects on human fibroblasts and cannot inhibit the neutralization of the antiviral effects of natural IFN-α by an antiserum directed against the interferon. Anti ACTH and Anti β-endorphin do not neutralize the antiviral effects of IFLrA, and radioimmunoassays of partially purified natural IFN-α and pure IFLrA do not reveal any evidence of α-MSH or β-endorphin-like material in the interferons. These results demonstrate an absence of functional and structural homology of natural and recombinant IFN-α with ACTH and β-endorphin.     

Class II genes of the human major histocompatibility complex. The DO beta gene is a divergent member of the class II beta gene family

A novel class II beta chain gene is described. This gene, tentatively called DO beta, displays considerably less polymorphism than beta genes of the DP, DQ, and DR loci. The nucleotide sequence of the DO beta gene is strikingly similar to that of the previously identified murine A beta 2 gene. The DO beta gene displays the same exon/intron organization as other beta genes although the fifth exon and the translated portion of the sixth exon are longer than in other genes. A striking feature of the amino acid sequence deduced from the DO beta gene sequence is the pronounced hydrophobicity of the NH2-terminal region. This feature distinguishes the putative DO beta chain from other class II beta chains and raises the possibility that DO beta chains may interact with an alpha chain that is structurally different from those of the DP, DQ, and DR loci. It further suggests that the putative DO molecule may have a function different from those of other class II antigens.