On the mechanism of ATP-induced shape changes in the human erythrocyte membranes: the role of ATP

In the preceding paper (Sheetz, M. and S.J. Singer. 1977. J Cell Biol. 73:638-646) it was shown that erythrocyte ghosts undergo pronounced shape changes in the presence of mg-ATP. The biochemical effects of the action of ATP are herein examined. The biochemical effects of the action of ATP are herein examined. Phosphorylation by ATP of spectrin component 2 of the erythrocyte membrane is known to occur. We have shown that it is only membrane protein that is significantly phosphorylated under the conditions where the shape changes are produced. The extent of this phosphorylation rises with increasing ATP concentration, reaching nearly 1 mol phosphoryle group per mole of component 2 at 8mM ATP. Most of this phosphorylation appears to occur at a single site on the protein molecule, according to cyanogen bromide peptide cleavage experiments. The degree of phosphorylation of component 2 is apparently also regulated by a membrane-bound protein phosphatase. This activity can be demonstrated in erythrocyte ghosts prepared from intact cells prelabeled with [(32)P]phosphate. In addition to the phosphorylation of component 2, some phosphorylation of lipids, mainly of phosphatidylinositol, is also known to occur. The ghost shape changes are, however, shown to be correlated with the degree of phosphorylation of component 2. In such experiment, the incorporation of exogenous phosphatases into ghosts reversed the shape changes produced by ATP, or by the membrane-intercalating drug chlorpromazine. The results obtained in this and the preceding paper are consistent with the proposal that the erythrocyte membrane possesses kinase and phosphates activities which produce phosphorylation and dephosphorylation of a specific site on spectrin component 2 molecules; the steady-state level of this phosphorylation regulates the structural state of the spectrin complex on the cytoplasmic surface of the membrane, which in turn exerts an important control on the shape of the cell.     

Geriatric medicine in Hull: a comprehensive service.

A partially age-related admission policy coupled with a "single-ward" scheme for treatment and rehabilitation was introduced by the Hull geriatric department in 1970. With rare exceptions, elderly patients needing hospital care have been admitted directly to the geriatric unit, and the proportion of the retired population admitted by the general physicians has been greatly reduced. The proportion of inpatients needing continuing care has been reduced to less than 20%, the mean length of inpatient stay has fallen to under 30 days, and separate long-stay wards are no longer needed. More than 91% of patients are admitted without preceding domiciliary assessment, and only 5-6% of admissions are transferred from other units within the area.     

RU486 blocks the secondary surge of follicle-stimulating hormone in the rat without blocking the drop in serum inhibin.

The stimulatory effect of progesterone on the release of the primary surges of serum LH and FSH is well characterized. Less is known about the relationship of progesterone to the secondary FSH surge. We used the antiprogesterone, RU486, to block the action of progesterone and studied the effects on the primary surges of LH and FSH, and especially on the secondary surge of FSH. Proestrous rats were treated with RU486 at 1,200 h. Rats were killed on proestrus and estrus, and serum levels of LH, FSH, and inhibin were measured. In all RU486-treated rats, the primary surges of LH and FSH were significantly attenuated, and the secondary FSH surge was completely abolished, despite a drop in inhibin levels following the primary surges. A high replacement dose of progesterone, delivered immediately after RU486 treatment, did not restore the primary surges of LH and FSH, or the secondary surge of FSH. These data suggest that other factors in addition to a drop in inhibin are responsible for producing the secondary FSH surge.     

Sperm cells of the pollen tubes of Brassica: Ultrastructure and isolation

Summary Sperm cells of pollen tubes grown both in vivo and in vitro form a male germ unit. Extensions from both sperm cells of each pollen tube are closely associated with the tube nucleus. A high yield (2.7 × 10⁴. 20 mg^–1 pollen grains germinated) of intact sperm cells was obtained following release by osmotic shock from pollen tubes grown in vitro. Structural integrity of isolated sperm was maintained by isolation at low temperature in an osmotically balanced medium. At 4° C many isolated sperm pairs were still enclosed within the pollentube inner plasma membrane. Sperm cells not enclosed within this membrane no longer remained connected as a pair. During isolation vesicles formed on the sperm cell surface from disruption of the fibrillar components bridging the periplasmic space. Both in the pollen tube and after isolation the sperm nucleus is in close association with at least one region of the sperm plasma membrane. Sperm isolated at room temperature showed the presence of nucleopores, and nuclei were euchromatic, instead of heterochromatic as in intact sperm in the pollen tube.     

Cytosolic and mitochondrial isoenzymes of branched-chain amino acid aminotransferase during development of the rat.

The isoenzymic forms of branched-chain amino acid aminotransferase in mitochondria of rat tissues were compared with the better-known cytosolic forms in order to find any regular pattern of expression of these isoenzymes during development. Mitochondria of all tissues examined except brain contained only a type-I isoenzyme differing from the cytosolic type-I isoenzyme in heat stability and activation by mercaptoethanol. Foetal and adult brain mitochondria contained isoenzymes type III as well as type I. The large excess of type-I isoenzyme in foetal liver was localized in mitochondria, apparently of haematopoietic cells. The activity of this isoenzyme declined precipitously (by 80%) from day 19 of gestation at the same period and rate as does the volume fraction of haematopoietic cells that are then leaving the liver. Cortisol treatment accelerated the loss of these cells, and proportionally accelerated loss of the mitochondrial isoenzyme I. A development succession of type-I isoenzyme by the unique type II of liver parenchymal cell cytosols could not be demonstrated, since small, about equal, amounts of types I and II were always present in cytosols of foetal and adult liver. Developmental succession of isoenzymes within tissues was limited to cytosols and was demonstrated by the presence of cytosolic isoenzyme III in foetal and newborn skeletal muscle and kidney, organs which contain only isoenzyme I in the adult.     

A scanning electron microscope study of healthy pecan tissues showing the presence or absence of internal fungal contamination

Summary Healthy pecan, Caryaillinoensis (Wang) Koch, tissue was obtained from an 8-year-old grafted Cherokee tree. Dormant buds were gathered and stored until spring growth. After rigorous surface sterilization, halves of both stored and freshly harvested dormant buds and of actively growing shoots were plated onto sterile PDA. Corresponding halves wre fixed in FAA and processed for scanning electron microscopy (SEM). All plated dormant buds (both stored and freshly harvested) showed presence internally of a fungus, and SEM studies revealed hyphalike strands similar to those of the isolated fungi within cells of those buds. The spring flush was sterile in culture, and strands were absent in SEM studies.     

Lifetime of fluorescence from light-harvesting chlorophyll a/b proteins. Excitation intensity dependence.

The fluorescence from a purified, aggregate form of the light-harvesting chlorophyll a/b protein has a lifetime of 1.2 +/- 0.5 ns at low excitation intensity, but the lifetime decreases significantly when the intensity of the 20-ps, 530-nm excitation pulse is increased above about 10(16) photons/cm2. A solubilized, monomeric form of the protein, on the other hand, has a fluorescence lifetime of 3.1 +/- 0.3 ns independent of excitation intensity from 10(14)-10(18) photons/cm2/pulse. We interpret the lifetime shortening in the aggregates and the lack of shortening in monomers in terms of exciton annihilation, facilitated in the aggregate by the larger population of interacting chlorophylls.     

Plasmodium falciparum: Synthesis of glycoprotein by cultured erythrocytic stages

The human malarial parasite, Plasmodium falciparum, incorporated significant radioactivity into glycoconjugates when cultured in the presence of [¹⁴C]- or [³H]glucosamine for 48 to 50 hr. Digestion of the labeled proteins with pronase and subsequent precipitation with absolute ethanol showed that 90 to 95% of the radioactive glucosamine was incorporated into the precipitated material. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the labeled macromolecules revealed eight bands with approximate molecular weights from 19,000 to 90,000 daltons.