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Biomedical subjects

A C Greenquist

Publications and source records attributed to A C Greenquist.

9 recordsLinked to original sources
PubMed1978

Bilayer balance and regulation of red cell shape changes.

Discocytic human red cells undergo discocyte-echinocyte and discocyte-stomatocyte transformations under the action of a wide variety of lipid-soluble anionic and cationic agents respectively. These shape transformations are explained by the bilayer couple hypothesis of Sheetz and Singer to be the result of preferential distribution of the anionic agents in the outer half of the bilayer and the cationic agents in the inner half of the bilayer. We demonstrate that echinocytogenic effects indeed occur when the naturally occurring phospholipid lysophosphatidylcholine (LPC) is localized in the outer half of the bilayer, and stomatocytogenic effects occur when LPC is in the inner half. However, in contrast to the bilayer couple hypothesis, our results show that simple equivalent membrane surface area expansion on each layer is insufficient to maintain the discocytic shape and there exists a differential concentration effect of LPC on the two halves of the bilayer.

Erythrocyte Membrane↗
PubMed1978

Marked reduction of spectrinin hereditary spherocytosis in the common house mouse.

In contrast to the disease in humans, hereditary spherocytosis in the common house mouse produces an extreme spherocytosis. The cells show a broad distribution in size ranging from microcytic to macrocytic. Of particular interest is the finding of a substantial reduction in the major membrane polypeptide called spectrin, supporting a critical role for this protein in the control of erythrocyte shape and membrane stability.

Animals↗
PubMed1978

The spectrin phosphorylation reaction in human erythrocytes.

Phosphorylation of spectrin in whole cells occurs on a single tryptic peptide and indicates a specific and limited modification of spectrin. Phosphorylation of spectrin in soluble extracts and isolated membranes is less specific. Diamide is an inhibitor of erythrocyte spectrin kinase and casein kinase. This agent also inhibits the restoration of biconcave morphology to metabolically depleted erythrocytes reincubated with adenosine.

Adenosine Triphosphate↗
PubMed1976

Phosphorylation in erythrocyte membranes from abnormally shaped cells.

Erythrocyte protein phosphorylation was examined in membrane preparations of 25 patients with hereditary spherocytosis (HS). Reduced phosphorylation in substrate polypeptides was observed in 22 HS erythrocyte membranes for both splenectomized and nonsplenectomized patients. A reduction in labeling was also observed in a polypeptide which was labeled only in the presence of cAMP. No reduction was observed in membranes from immunologically acquired spherocytosis cells or from cells from patients with hereditary elliptocytosis. Heating membranes to 45 degrees C caused negligible inhibition of membrane protein phosphorylation, while heating to 50 degrees C extensively inhibited phosphorylation. Dephosphorylation of membrane protein that occurred in isolated membranes was not dependent upon cAMP.

Cyclic AMP↗
PubMed1976

Stabilization of the shape of sickled cells by calcium and A23187.

Evaluation of the role of calcium in irreversible sickling has been approached by treating sickled cells with calcium and the ionophore A23187. A calcium-dependent stabilization of the sickled cell shape was observed after reoxygenation of cells in the presence of ionophore. At low calcium concentrations, this retention of sickled shape was maintained for periods up to 1 hr. However, the morphology of the oxygen-stable sickled cells was like that of deoxygenated sickle cells and significantly different from the characteristic morphology of native irreversibly sickled cells (ISCs). Because the stabilized cells did not fulfill the morphological criterion for ISCs, the shape-stabilizing effect of calcium in this system did not provide additional support for the hypothesis that calcium accumulation was the determining factor in ISC generation.

Anemia, Sickle Cell↗
PubMed1975

Immunochemical studies on factor V.

Native bovine factor V exhibits a molecular weight of 300000 as determined by gel filtration of untreated plasma. Highly purified factor V exhibits multiple molecular weight forms which range from small active fragments to aggregates of several million which are generated during the purification on cellulose phosphate. Isoelectric focusing on a single high-molecular-weight species produced a single protein and activity peak at pH 4.65. Factor V activity is associated with each protein band observed following polyacrylamide gel electrophoresis. Antisera to factor V prepared in rabbits produces a time-dependent and concentration-dependent inhibition of factor V activity in plasma and purified factor V. The multiple molecular weight forms of factor V appear equivalent upon immunodiffusion and on immunoelectrophoresis migrate as an alpha globulin between albumin and fibrinogen. Immunoprecipitation arcs are equivalent in plasma and serum. Factor V consists of two major types of subunits, a light chain (73000), aggregates of which form the high-molecular-weight species, and a heavy chain (125 000). Using preparations containing one or both chains isolated by disc gel electrophoresis, antiserum was shown to contain two families of antibodies, one against each subunit. Cross reactivity with both light and heavy chain antigens is observed in sheep and goat but not monkey or human plasma. The antisera also neutralized goat and sheep factor V activity.

Animals↗
PubMed1975

Bovine factor v: a calcium-containing metalloprotein.

Although coagulation factor Xa requires Ca2+ for binding to phospholipid, factor V, the other protein component in the prothrombinase enzyme complex, binds tightly to phospholipid in the absence of Ca2+. To explore the possibility that calcium might be present in the fact V molecule, the effect of several chelators, including oxalate, citrate, pyrophosphate, and EDTA, on factor V activity has been studied. A time- and concentration-dependent inhibition of factor V which reflects the respective association constants for calcium of each chelator is observed. The inhibition can be prevented by the prior addition of calcium and manganese but not magnesium. Reversal of the activity loss can be accomplished at high protein concentrations by the addition of calcium, the removal of the chelator by gel filtration, or an increase in temperature. Factor V contains 1 g atom of calcium per 300,000 daltons which is not removed by incubation with EDTA under nondenaturing conditions. Thus, the inhibition by EDTA is due to binding to calcium associated with factor V. In 8 M urea, EDTA can remove over 80% of the calcium, demonstrating the importance of the native structure in maintaining the calcium binding site. Prior binding of phospholipids to factor V prevents inhibition by EDTA. The results suggest that phospholipids complex at the calcium site on the factor V metallopretein.

Animals↗