Isolation of plasma membranes from Ehrlich ascites tumor cells Influence of amino acids on (Na + K)-ATPase and K-stimulated phosphatase

A method was developed for isolating plasma membranes from Ehrlich ascites tumor cells. The plasma membranes appeared as highly irregular shrunken sacs or ghosts. Enzymatic characterization of the plasma membranes showed them to be high in (Na⁺ + K⁺-ATPase activity and K⁺-stimulated phosphatase activity. A detailed study showed that both of these latter enzymic functions were stimulated by various amino acids. Such stimulation occurred in the 1–15 mM range of amino acids and was most effective for aromatic species, e.g. phenylalanine and histidine. The amino acid stimulation, which appeared to show little or no stereospecificity, was eliminated by a one carbon separation of NH₂ and COOH groups. Since the metal chelating agent EDTA was also effective in mimicking the stimulation by amino acids, and since a mild washing procedure did not render membranes insensitive to subsequent amino acid or EDTA stimulation, it is proposed that the operation of the (Na⁺ + K⁺)-ATPase (and K⁺-stimulated phosphatase) is to some extent controlled by a tightly bound metal. The possible physiological function of an amino acid-regulated transport ATPase is discussed.     

Utilization of transferrin-bound iron by Listeria monocytogenes

Abstract It has been demonstrated that under iron-restricted conditions, Listeria monocytogenes can utilize iron-loaded transferrin (Tf) from a range of species as its sole source of iron for growth. Human transferrin conjugated to horseradish-peroxidase (HRP-Tf) bound directly to whole cells of L. monocytogenes . This binding was blocked by apotransferrin indicating that the receptor can bind transferrin in either the iron-bound or iron-free form. Transferrin-binding was not host specific because both bovine and equine transferrin inhibited the binding of HRP-conjugated human transferrin. SDS-PAGE and Western blotting of bacterial surface extracts revealed the presence of a transferrin-binding protein of approximately 126 kDa.     

CP12: a small nuclear-encoded chloroplast protein provides novel insights into higher-plant GAPDH evolution

Higher-plant chloroplast NAD(P)-glyceraldehyde 3-phosphate dehydrogenase (NAD(P)-GAPDH; EC 1.2.1.13) is composed of two different nuclear-encoded subunits, GAPA and GAPB, forming the highly active heterotetrameric A₂B₂ enzyme. The main difference between these two subunits is a C-terminal extension of about 30 amino acid residues of GAPB. We present cDNA clones for a nuclear-encoded chloroplast protein from pea, spinach and tobacco, which we have named CP12. The mature protein consists of only 74, 75 and 76 amino acid residues, respectively and contains two domains with significant homology to the C-terminal extension of GAPB. Affinity chromatography approaches reveal also a specific interaction between CP12 and chloroplast GAPDH. Northern blot analysis indicates that CP12 is, like plastid GAPDH, expressed in green and also in etiolated leaves. Further homology is observed between CP12 and ORF3, an open reading frame located in the hox gene cluster of Anabaena variabilis. This gene cluster encodes the subunits of the bidirectional NADP⁺-dependent [NiFeS] dehydrogenase. We propose therefore a common evolutionary origin of CP12 and higher-plant chloroplast GAPDH subunit GAPB from the cyanobacterial ORF3.     

Complex effects of grazing treatment on an annual in a species-poor grassland community

Abstract. The effects of grazing upon the establishment, survival, growth and reproduction of a grassland annual Geranium dissectum growing in a sward dominated by grasses were examined in a replicated grazing experiment with sheep. Seeds were sown in both summer and autumn, and grazing was controlled to produce two levels of grazing in winter, two levels in spring, and two in summer, combined in a 2 x 2 x 2 factorial experimental design. Higher intensities of grazing in the period immediately before emergence benefitted plant establishment, but subsequent survival showed many interactions between factors, demonstrating that under certain conditions and at certain times grazing was detrimental. It is suggested that the frequency of G. dissectum in the grassland was low because the heavy grazing conditions that foster seedling emergence also jeopardize subsequent survival. This may also be why productive grassland communities in general contain few palatable dicots.     

Factors influencing the growth of alveolar type II epithelial cells isolated from rat lungs

Primary cultures of isolated alveolar type II cells have been established. Under appropriate conditions, these epithelial cells can be subcultured at least nine times. Using standard assay procedures, effects of growth factors or inhibitors can be studied. The alveolar type II cells show a marked response to both serum and growth factors in tissue culture. Either epidermal growth factor (EGF) or human urine gives an increase in thymidine incorporation (2-fold and 10-fold, respectively). The growth factor(s) in urine appears to be different from urogastrone (human EGF). The response to urine is several-fold greater than the response to a saturating concentration of mouse EGF alone. Mouse EGF added to urine does not increase the activity of urine. The period during which the alveolar type II cells respond to the growth factor(s) in urine is limited to early passages of the cells. Alveolar type II epithelial cells produce growth inhibitors in culture. Inhibitors are produced in the growth medium in either the presence or absence of serum. The concentrated inhibitor, although very unstable, gives up to a 50% inhibition of thymidine incorporation when assayed on sparse or crowded alveolar type II cells.     

The nature of quantittative genetic variation revisited: Lessons from Drosophila bristles

Most characters that distinguish one individual from another, like height or weight, vary continuously in populations. Continuous variation of these ‘quantitative’ traits is due to the simultaneous segregation of multiple quantitative trait loci (QTLs) as well as environmental influences. A major challenge in human medicine, animal and plant breeding and evolutionary genetics is to identify QTLs and determine their genetic properties. Studies of the classic quantitative traits, abdominal and sternopleural bristle numbers of Drosophila, have shown that: (1) many loci have small effects on bristle number, but a few have large effects and cause most of the genetic variation; (2) ‘candidate’ loci involved in bristle development often have large quantitative effects on bristle number; and (3) alleles at QTLs affecting bristle number have variable degrees of dominance, interact with each other, and affect other quantitative traits, including fitness. Lessons learned from this model system will be applicable to studies of the genetic basis of quantitative variation in other species.