Electric birefringence of recombinant spectrin segments 14, 14-15, 14-16, and 14-17 from Drosophila alpha-spectrin

Members of the spectrin protein family can be found in many different cells and organisms. In all cases studied, the major functional role of these proteins is believed to be structural rather than enzymatic. All spectrin proteins are highly elongated and consist mainly of homologous repeats that constitute rigid segments connected in tandem. It is commonly believed that the details of the spectrin function depend critically on the flexibility of the links between the segments. Here we report on a work addressing this question by studying the transient electric birefringence of recombinant spectrin fragments consisting of segments 14, 14-15, 14-16, and 14-17, respectively, from Drosophila alpha-spectrin. Transient electric birefringence depends sharply on both molecular length and flexibility. We found that the birefringence relaxation time of segment 14 measured at 4 degrees C, but scaled to what is expected at 20 degrees C, equals 16 ns (+/-15%) at pH 7.5 and ionic strength 6 mM. This is consistent with this single segment being rigid, 5 nm long and having an axial ratio equal to about two. Under the same conditions, segments 14-15, 14-16 and 14-17 show relaxation times of 45, 39 and 164 ns (all +/-20%), respectively, scaled to what is expected at 20 degrees C. When the temperature is increased to 37 degrees C the main relaxation time for each of these multisegment fragments, scaled to what is expected at 20 degrees C, increased to 46, 80, and 229 ns (all +/-20%), respectively. When the ionic strength and the Debye shielding is low, the dynamics of these short fragments even at physiological temperature is nearly the same as for fully extended weakly bending rods with the same lengths and axial ratios. When the ionic strength is increased to 85 mM, the main relaxation time for each of these multisegment fragments is reduced 20-50% which suggests that at physiological salt and temperature conditions the links in 2-4-segment-long fragments exhibit significant thermally induced flexing. Provided that the recombinant spectrin fragments can serve as a model for native spectrin, this implies that, at physiological conditions, the overall conformational dynamics of a native spectrin protein containing 20-40 segments equals that of a flexible polymer.     

Volume 14, 1998

World Journal of Microbiology and Biotechnology -     

Plant uptake of 14C-EDTA, 14C-Citrate, and 14C-Histidine from chelator-buffered and conventional hydroponic solutions

Chelator-buffered hydroponic solutions provide low and buffered free-metal concentrations and allow the easy calculation of nutrient species expected in these solutions. Some researchers suspect that the solutions allow plant uptake of chelates and that this uptake explains the failure of the free-ion activity model using these solutions. To determine the amount and method of chelate uptake, swiss chard was grown in solution culture in growth chambers for about three wks and then transferred to solutions containing ¹⁴C-EDTA, ¹⁴C-citrate, or ¹⁴C-L-histidine for a 21-hour assay. Much higher root and shoot ¹⁴C were found from treatments containing metabolites histidine (2706097 shoot Bq ¹⁴C) or citrate (2241953 shoot Bq ¹⁴C) than EDTA (280110 shoot Bq ¹⁴C). Passive transpirational flow could explain all of the EDTA uptake, but active uptake would be required to explain most of the citrate and histidine uptake even assuming some adsorption of ligand bound to roots. Swiss chard grown in solutions with the same total EDTA concentrations, but different amounts of Fe bound to EDTA, had 3-fold differences in root and shoot ¹⁴C concentrations. In a second experiment, swiss chard roots removed more EDTA from solutions containing mostly M-EDTA⁰ than M-EDTA^1- or M-EDTA^2- (288140, 245051, and 192559 Bq ¹⁴C, respectively) suggesting plant selectivity for EDTA and a non-apoplastic route of uptake or an effect resulting from root cell-wall adsorption. Results indicated buffering of metals by ligands allowed some ligand uptake with much more uptake occurring with metabolites citrate and histidine than EDTA. A passive or indiscriminate form of uptake does not appear to explain all EDTA uptake with a selectivity by swiss chard for M-EDTA complexes of lower charge.     

Index,Volume 14, 2001

Abstract

Companion animal abuse is a universal phenomenon recorded since the earliest times. The lack of standardized definitions concerning companion animal abuse impedes research and reporting on the subject. In order to address this problem a typology of companion animal abuse is proposed for general application to identify the different types of abuse. Analysis of the records of the Society for the Prevention of Cruelty to Animals in South Africa indicated the usefulness of such a typology. Education based on the typology may contribute to the prevention of companion animal abuse.     

Assimilative Pathway of Methanol in Candida sp. Incorporation of 14C-Methanol, 14C-Formaldehyde, 14C-Formate and 14C-Bicarbonate into Cell Constituents

1. The incorporation of ¹⁴C-methanol, ¹⁴C-formaldehyde, ¹⁴C-formate and ¹⁴C-bicarbonate into a methanol-utilizing yeast, Candida N–16, was examined by paper-chromato-graphy and radioautography.

2. At the earliest time period examined, the highest percentage of radioactivity fixed from ¹⁴C-methanol or ¹⁴C-formaIdehyde into methanol-grown cells was found in fructose phosphate. The percentage distribution of radioactivity in fructose phosphate decreased as time elapsed. The radioactivity fixed from these compounds into glucose-grown cells was negligible compared with that fixed into methanol-grown cells.

3. The incorporation of ¹⁴C-formate into methanol-grown cells was extremely low. The highest percentage of radioactivity fixed for short time incubation was found in serine. The incorporation pattern of glucose-grown cells was similar to that of methanol-grown cells.

4. At the earliest time period, over 70% of radioactivity fixed from ¹⁴C-bicarbonate into methanol- or glucose-grown cells was found in aspartate.

5. These results suggest that in Candida N–16 methanol is specifically assimilated by a route with hexose phosphate as a primary stable intermediate.

     

Contents Volume 14, 1988

Summary

Within the unpaired testis, spermatogonia, spermatocytes, spermatids and spermatozoa were found. In early spermatids, mitochondria take perinuclear positions and centrioles a diplosomal arrangement. Rootlet-like striated differentiations occur in slightly more advanced stages. Then a conical cytoplasmic projection develops, supported by a single row of closely spaced microtubules. At this stage of maturation, giant Golgi stacks occur within the cytoplasm of the cytophore which is rich in different elongate structures and oval dense bodies. With progressive differentiation, the nucleus elongates and its chromatin condenses into twisted lamellae. Two centrioles, which change their diplosomal configuration and come to lie in line to each other, and rootlet-like structures remain near the tip of the median cytoplasmic outgrowth. Mitochondria start to fuse into a single long cylindrical mitochondrial rod extending beside the lengthening nucleus. Bone-shaped rods, smaller dense sticks and dense bodies migrate into the outgrowth. Spermatozoa are totally ensheathed by cortical microtubules. These tubules show different arrangements along the cell body. The thread-like nucleus extends along the cell, the first quarter excepted, whereas the single mitochondrion extends over two thirds of the cell. Two strings with linearly arranged oval dense bodies run in the median to post-median cell segment; four rows of bone-shaped rods and two rows of smaller electron-dense sticks extend from the frontal end up to the beginning of the last third of the cell. All the different longitudinal cords run in the gaps between 4 sets of microtubules. Ciliary axonemes or lateral bristles were not observed. The present findings substantiate the hypotheses, that spermatozoa in the Macrostomida are aciliate and that Myozona takes an isolated position within the Macrostomidae. The occurrence of two centrioles, which come to lie in line to each other and which stay in the tip of the cytoplasmic outgrowth in spermatids, may indicate that biciliate spermatozoa are characteristic for the Rhabditophora (= Macrostomorpha+Trepaxonemata) and not an evolutionary novelty of the Trepaxonemata.     

Clinical findings in an Arab boy with ring (14)(mos 46,XY,r(14)/45,XY,-14)

A five-month male Arab child with clinical features of ring(14) is reported. He had recurrent seizures and chest infections, microcephaly, elongated face, short palpebral fissures, broad nasal bridge, long philtrum, fish-like mouth with thin lips, micrognathia, low-set ears and retinal pigmentation with yellow-white spots on the maculae. In addition brachydactyly of fingers and toes, hypoplastic scrotum and mental deterioration were present.