摘要:

AbstractThe hepatic mechanism for detoxication of ammonia formed during amino acid gluconeogenesis in uricotelic vertebrates requires the intramitochondrial synthesis of glutamine by glutamine synthetase. This glutamine then serves as a precursor of uric acid in the cytosol. The evolutionary development of uricoteley thus required the localization of glutamine synthetase in liver mitochondria. The mechanism for the mitochondrial import of glutamine synthetase in uricotelic vertebrate liver is not yet known. Tortoises, extant relatives of the stem reptiles, possess both the ureotelic and uricotelic hepatic systems. It therefore seems likely that the genetic events allowing the mitochondrial localization of glutamine synthetase in liver occurred in the amniote amphibian ancestors of the stem reptiles. The selection of ureoteley by the theropsids and of uricoteley by the sauropsids were major events in the divergence and subsequent evolution of these two lines. Once established in the sauropsid line, uricoteley has persisted through to the higher reptiles, crocodilians, and birds. Uricoteley was in part responsible for the radiation of the archosaurs during the Triassic as a water‐conserving mechanism in the adult, thereby allowing them to invade the arid environments of that period. Contrary to dogma, uricoteley was probably of minor significance in the development of the cleidoic egg. Neither mammalian nor avian embryonic liver tissues catabolize amino acids to any great extent, so it is inappropriate to attribute to them a kind of “waste” nitrogen metab

ISSN:0022-104X    

DOI:10.1002/jez.1402430302

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1987

数据来源: WILEY

摘要:

AbstractThe effects of hyperosmotic stress on amino acid metabolism have been examined inAcanthamoeba castellaniiincubated in a defined growth medium. Following hyperosmotic shock, the rapid appearance in the medium of previously ingested proline indicated a rapid release of pinosome contents induced by osmotic dehydration. Initially endocytotic uptake and protein synthesis were both markedly inhibited, but they recovered over the following hours. Total cell proteins decreased by 20% within 30 minutes after hyperosmotic stress, and this decrease was concomitant with a rapid accumulation of free ninhydrin‐positive substances.Following a hyperosmotic shock, free alanine, glutamate, and proline transiently accumulated, in this sequence. Aminooxyacetate prevented the accumulation of alanine while greatly stimulating that of glutamate, but its effect on proline accumulation was small. In cells incubated with radioactive alanine, the accumulation of free alanine proceeded mostly from unlabeled precursors and coincided with a high rate of radioactive glutamate synthesis. This newly synthesized glutamate was extensively converted into proline, while proline synthesis from ornithine was barely stimulated. During acclimation to hyperosmotic conditions, osmoregulatory mechanisms inA. castellaniiappear to rely only transiently on free amino acids, particularly on those whose access to main metabolic pathways is not allosterically regulate

ISSN:0022-104X    

DOI:10.1002/jez.1402430303

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1987

数据来源: WILEY

摘要:

AbstractThe mode of action of external ATP on the contractile vacuole ofAmoeba proteushas been examined. ATP and, to a lesser extent, some other polyphosphates, interact with calcium at nonhydrolyzing membrane sites. This induces an increase of output of the contractile vacuole provided sodium is present in the medium. A long‐lasting reversible membrane depolarization occurs in the presence of ATP. Results are discussed in the light of theories describing the contractile vacuole as the principal sodium‐excreting organelle in freshwater Proto

ISSN:0022-104X    

DOI:10.1002/jez.1402430304

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1987

数据来源: WILEY

摘要:

AbstractExtracts from integumentary tissues of the Bermuda land crab,Gecarcinus lateralis, degraded proteins extracted from the membranous layer (ML), the innermost layer of the exoskeleton that serves as the interface between epidermal cells and calcified exoskeleton. Separation of the extracts by HPLC hydrophobic chromatography and characterization using125I‐casein as substrate identified two peaks of degradative activity. The activities showed pH optima of 7 to 8, were sensitive to inhibitors of cysteine proteinases, and required the reducing agent, dithiothreitol, for activity, indicating that they are alkaline cysteine proteinases (ACPs). The pH optima of ACPs I and II indicated that they could function in the slightly alkaline extracellular environment of the proecdysial animal when the old exoskeleton is broken down. Although ACPs I and II are distinctly different from other crustacean cysteine proteinases (CP) they are similar to a CP activity present in extracts from the ML. A 23‐kDa protein from the ML was particularly susceptible to degradation by these enzymes. Activity of these enzymes in the extracellular environment might be controlled by the concentration of reducing agents as they are inactive unless in a reduced st

ISSN:0022-104X    

DOI:10.1002/jez.1402430305

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1987

数据来源: WILEY

摘要:

AbstractSome species of ciliated protozoans vary their body volume when fed on preys of different sizes. This peculiarity has offered us the opportunity to examine the relationship between changes in cell volume, amount of macronuclear DNA (maDNA), and cell division rates in subclones derived from a single clone of the ciliateBlepharisma japonicum(Order Heterotrichida). Our results demonstrate that food‐induced size changes in this single‐celled organism are accompanied by substantial changes in maDNA content and in reproduction (cell division) rate. We find a strong, direct linear correlation between cell volume and maDNA quantity, and an inverse linear correlation between cell volume and reproduction rate. No correlation between cell reproduction rate and maDNA amount was found. We conclude that food‐induced coordinate change in cell volume, maDNA content, and cell division rate in this organism may be an effective mechanism for rapid phenotypic change in response to variable environmental condi

ISSN:0022-104X    

DOI:10.1002/jez.1402430306

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1987

数据来源: WILEY

摘要:

AbstractInTriturus cristatus carnifex(Laurenti) newts rendered to tally anemic by treatment with acetylphenylhydrazine (APH) diluted in their tank water (25 mg/liter for 48 hours, with four changes) the recovery of erythron occurs through periodic cycles of mitotic activity in the erythropoietic tissue. These cycles determine a marked increase in blood erythrocyte concentration at regular intervals of about 1 month. The consequence of this trend is the alternation of ferritin and hemosiderin accumulation phases during periods of stasis with iron mobilization phases during periods of erythropoietic activity, which is particularly evident in the Kupffer cells of the liver. Iron mobilization and erythropoietic activity are strictly related to the periodic hypertrophy of some Bowman's capsule cells in the renal corpuscle, which were previously denominated “lactate sensitive cells” (LSC). The histochemistry, location, and behavior of LSC indicate that they are probably the site of erythropoietin production in the n

ISSN:0022-104X    

DOI:10.1002/jez.1402430307

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1987

数据来源: WILEY

摘要:

AbstractThe purpose of this investigation was to determine whether measurable characteristics of furrow activity were affected when the distance between the asters was manipulated. The mitotic apparatus of cleavingEchinarachnius parmaeggs was broken by passing the egg several times through a constricting pipet nozzle. Manipulated eggs were then confined in 80 μm i.d. silicone rubber capillaries. When the astral pairs developed before second cleavage, the distances between the pairs often differed. When the difference between interastral distances was 8.6 μm or less, furrows developed in the normal relation to both astral pairs within 1 minute in 31 of 35 cases. When the difference of interastral distances was greater than 8.6 μm, the furrow appeared first in association with the smaller distance in 53 of 54 cases. In all (24) cases in which the rates of progress of each astral pair were measured, the furrow formed between the closer astral pair progressed more rapidly when the distance was greater than 8.6 μm. No significant correlation between the rates of furrow progress and the magnitude of interastral distances measured 4 minutes before the beginning of furrowing could be demonstra

ISSN:0022-104X    

DOI:10.1002/jez.1402430308

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1987

数据来源: WILEY

摘要:

AbstractAlthough recent experiments on pattern formation during amphibian limb regeneration have relied on the use of triploid marked cells, the purity of the triploid donor has not been proven. To test the purity of the donor, blood (which contains noncycling nucleated red blood cells) was collected from the gills of 12 pressure‐induced triploid axolotls from two unrelated spawnings. Blood was also collected from 12 untreated sibling animals to serve as diploid controls. The blood samples were placed into a propidium iodide stain solution that had been adjusted to amphibian tonicity by the addition of distilled water. Samples were analyzed on an EPICS V (Coulter) flow cytometer. A minimum of 20,000 cells were analyzed in each sample at a flow rate that did not exceed 1,000 cells/second. In the diploid group, 88.6% of the cells were collected in channels of the DNA histogram corresponding to a 2C G1/G0DNA content (channel 71±10) and 0.9% were collected in channels corresponding to a 3C G1/G0DNA content (channel 106±10). In the triploid group, 99.2% of the cells were collected in nondiploid channels and only 0.8% were collected in channel 71±10. Utilizing the average peak channel number for the diploid group of 12 animals an average haploid channel number of 35 was calculated. The triploid group of animals exhibited DNA ploidy that averaged one haploid channel number above that of the diploid group. Based on forward angle light scatter, nuclei obtained from triploid red blood cells were observed to be larger than nuclei from diploid blood. Preliminary data are presented which demonstrate that the ploidy characteristics of solid tissues (brain, cornea, spleen, muscle, and limb blastemal mesenchyme) agree with those presented for b

ISSN:0022-104X    

DOI:10.1002/jez.1402430309

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1987

数据来源: WILEY

摘要:

AbstractEpithelial‐mesenchymal interactions play important roles in the development of the vertebrate integument with its diverse appendages. As a result of these interactions, specific morphogenetic events occur which result in the formation of distinct epidermal appendages. Following the early morphogenetic events involving cell proliferation and movement, other developmental events such as stratification, histotypic differentiation, and terminal cytodifferentiation occur in the epidermis. Using the common lizardAnolis carolinensis, we are seeking to obtain a better understanding of the relationship between the various developmental events and the expression of α and β keratins, with the aim of eventually understanding the mechanisms by which tissue‐specific keratinization patterns are established in the integument. As a first step, we have used immunoblot analyses and indirect immunofluorescence procedures with antisera specific for either α or β keratins to determine the temporal and spatial appearance of these keratins at specific developmental stages. We have found that: 1) There are relatively low molecular weight α keratin polypeptides present in the epidermis early in development as morphogenesis is taking place. 2) After morphogenesis occurs and histogenesis is well under way, the α keratins which characterize the adult epidermis appear. 3) Only α keratins are found in the basal cells of all regions of the epidermis. 4) β keratins are found only in the suprabasal layers of well‐developed scales and show region‐specific distribution in ove

ISSN:0022-104X    

DOI:10.1002/jez.1402430310

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1987

数据来源: WILEY

摘要:

AbstractThe absence of DNA from the blood serum of the toadBufo arenarumwas confirmed by classical colorimetric techniques and by a new method which allows differentiation between DNA and the glycosaminoglycans (GAG). A component of serum which had some of the properties of DNA was identified as a GAG. This component gave positive reactions in colorimetric assays for DNA, but the absorption spectra were completely different from those of authentic DNA. The compound was also not hydrolized at all by treatment with deoxyribonuclease.

ISSN:0022-104X    

DOI:10.1002/jez.1402430311

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1987

数据来源: WILEY