Phosphorylation of lens membrane: identification of the catalytic subunit of Na+, K+-ATPase

Receptor mediated endocytosis appears to depend on the action of a transglutaminase (TGase). Endocytosis can be induced in intact human RBC by the action of several classes of drugs. We tested the hypothesis that drugs acted by stimulating TGase activity. Of the endocytosis inducing drugs tested, neither primaquine nor vinblastine nor chlorpromazine enhanced TGase activity. We next tested the hypothesis that TGase activity was required for drug endocytosis in RBC by adding known TGase inhibitors. Paradoxically, m-Dansyl cadaverine, the most potent TGase inhibitor, produces endocytosis in human RBC. Therefore despite apparent striking morphologic similarities, drug induced endocytosis in RBC appears to proceed via different mechanisms from those involved in receptor mediated endocytosis in other cells.In the receptor-mediated endocytosis of some hormones and growth factors, it appears that the receptor-ligand complex forms clusters over clathrin coated pits which are then internalized as endocytic vacuoles. Both the clustering and internalization of ligands are inhibited by a variety of agents shown to inhibit transglutaminase (TGase) and it is therefore proposed that TGase participates in receptor-mediated endocytosis (1–3). Human erythrocytes undergo endocytosis when exposed to drugs like primaquine, chlorpromazine, and vinblastine (4), all of which are amphipathic cations (4). However, the mechanism of drug action is not known nor is it clear that this is a form of receptor-mediated endocytosis (4). Furthermore, clustering of receptors can occur in neonatal but not adult human RBC (5). TGase has been measured in human red cells (6) although its physiologic role is unknown. Like all TGases, it is calcium dependent (6,7), and primaquine induced red cell endocytosis is enhanced by Ca⁺⁺ addition (8). Therefore, we tested the hypothesis that TGase participates in drug induced endocytosis in intact human red cells.     

Studies on the origin of the near-infrared (800–900 nm) absorption of cytochrome c oxidase

Data are presented which were collected in the course of the past ten years and bear on the correlation of absorbance at 800 nm and the EPR signal at g = 2 (‘copper signal’) of cytochrome c oxidase in various states of oxidation and ligation. Both EPR and optical reflectance spectra were obtained at low temperature (?170 to ?190°C). For some sets of samples spectra were recorded in the range 500–1100 nm. A particular effort was made to study this correlation with what are called ‘mixed valence’ states (Greenwood, C., Wilson, M.T. and Brunori, M. (1974) Biochem. J. 137, 205–215), when cytochrome a and the EPR-detectable copper are thought to be oxidized and the other components reduced and vice versa. These data show no evidence that the copper component of cytochrome oxidase which has so far not been detected by EPR makes a contribution to the absorption between 800 and 900 nm exceeding 10–15% of the total, which is close to or within the error of the respective measurements. For the various states of the oxidase examined in this work the 700–800 nm region did not appear to be more useful than the 800–900 nm region for determining the state of the EPR-undetectable copper in a reliable way. These conclusions are in agreement with results presented previously from other laboratories concerning the relationship of optical (approx. 800 nm) and EPR spectroscopic (g = 2) data obtained with the enzyme.     

A routine method for quantitative determination of soluble carbohydrates in small samples of plant material with gas-liquid chromatography

Aluminium in human tissue samples has been determined by atomic absorption spectrophotometry using the nitrous oxide-acetylene flame and the graphite furnace atomizer. The two methods are compared. Flameless atomic absorption was found superior when standard addition was applied. A routine method is thus described in detail in which aluminium levels down to 0.1 mg/kg of freeze-dried tissue and 0.01 mg/liter of serum can be determined.     

The effect of sodium on inorganic phosphate- and p-nitrophenyl phosphate-facilitated ouabain binding to (Na+ + K+)-activated ATPase.

The effect of the hydrolysis product Pi and the artificial substrate p-nitrophenyl phosphate (p-nitrophenyl-P) on ouabain binding to (Na+ + K+)-activated ATPase was investigated. The hypothesis that (Mg2+ + p-nitrophenyl-P)-supported ouabain binding might be due to Pi release and thus (Mg2+ + Pi)-supported could not be confirmed. The enzyme . ouabain complexes obtained with different substrates were characterized according to their dissociation rates after removal of the ligands facilitating binding. The character of the enzyme . ouabain complex is determined primarily by the monovalent ion present during ouabain binding, but, qualitatively at least, it is immaterial whether binding was obtained with p-nitrophenyl phosphate or Pi. The presence or absence of Na+ during binding has a special influence upon the character of the enzyme . ouabian complex. Without Na+ and in the presence of Tris ions the complex obtained with (Mg2+ + Pi) and that obtained with (Mg2+ + p-nitrophenyl-P) behaved in a nearly identical manner, both exhibiting a slow decay. High Na+ concentration diminished the level of Pi-supported ouabain binding, having almost no effect on p-nitrophenyl phosphate-supported binding. Both enzyme . ouabain complexes, however, now resembled the form obtained with (Na+ + ATP), as judged from their dissociation rates and the K+ sensitivity of their decay. The complexes obtained at a high Na+ concentration underwent a very fast decay which could be slowed considerably after adding a low concentration of K+ to the resuspension medium. The most stable enzyme . ouabain complex was obtained in the presence of Tris ions only, irrespective of whether p-nitrophenyl phosphate of Pi facilitated complex formation. The presence of K+ gave rise to a complex whose dissociation rate was intermediate between those of the complexes obtained in the presence of Tris and a high Na+ concentration. It is proposed that the different ouabain dissociation rates reflect different reactive states of the enzyme. The resemblance between the observations obtained in phosphorylation and ouabain binding experiments is pointed out.     

Light, fluorescence and electron microscopic studies of rabbit subclavian glomera.

The subclavian glomera (aortic bodies) of young New Zealand white rabbits were studied with the light, fluorescence, and electron microscopes. Two cell types were identified: type I, granule-containing (chief) cells, and type II, agranular (sustentacular) cells. The type I cells possessed large nuclei, the normal complement of cytoplasmic organelles and numerous electron-opaque cytoplasmic granules. The type II cells were agranular with attenuated cytoplasmic processes which partially or completely ensheathed the type I cells. The glomera were well vascularized. Capillary endothelial cells contained numerous pinocytotic vesicles, but few fenestrae. Two profiles of nerve terminals were observed. One, apposing the type I cells, contained numerous electron-lucent vesicles, several dense-cored vesicles, mitochondria and possessed membrane specializations resembling those usually observed in synaptic zones. The other profile contained abundant mitochondria and a few electron-lucent and dense-cored vesicles. Structural specializations were not observed on the apposed membranes of these terminals or adjacent to type II cells. Fluorescence histochemistry revealed an intense yellow-green fluorescence in the glomera, which indicated the presence of biogenic amines, possibly primary catecholamines or an indolamine. The electron-opaque granules observed in the type I cells were believed to be the storage sites for these amines. The subclavian glomera were found to be morphologically similar to the carotid body which is a known chemoreceptor.     

Population recovery of alien black rats Rattus rattus: A test of reinvasion theory

Reinvasion of pest animals after incomplete control is a major challenge for invasive species management, yet little is known about the behavioural and demographic categories of reinvaders or the mechanisms that drive population‐level responses to control. To understand the fine‐scale mechanisms of reinvasion, we examined changes in demography, movements and activity patterns of reinvading alien black rats Rattus rattus in the short (4 weeks) and longer term (3 months) following localised experimental pest removal. Using recovery and invasion theory, we tested three hypothesised mechanisms of reinvasion: the ‘in situ effect’, the ‘trickle effect’ and the ‘vacuum effect’. We created space for reinvasion by removing black rats from the core of replicate 1‐ha plots (short‐term experiment) and later by removing animals from the entire plot (longer‐term experiment). Reinvaders were characterised as dispersing juveniles, floaters or neighbours. Radio‐tracking quantified home range changes for adjacent resident animals (short‐term experiment only). In the short term, there was no net influx of rats after targeted removal. Radio‐tracked residents’ movements were highly variable and displayed no directional changes after nearby conspecifics were removed. However, in the longer term, removal led to slow population recovery through a mix of reinvading floaters, dispersing juveniles and shifting residents. These responses best support a hypothesis of reinvasion through a trickle effect, with rats being extremely mobile and having a high degree of population turnover, even in untreated sites. Our findings provide the first test of reinvasion theory at a small scale, demonstrating the importance of understanding the differing categories of reinvaders and mechanisms of reinvasion after population control. These mechanisms drive the rate of population recovery and, in turn, should help determine which strategy of pest control should be used, and the frequency with which they are implemented, in order to slow the recovery of pest populations.