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Biomedical subjects

B Reimann

Publications and source records attributed to B Reimann.

At least 37 records · Page 2Linked to original sources
PubMed1987

Maturation dependence of the turnover of phosphatidylinositides in rabbit red blood cells.

"Pulse-chase" experiments with erythrocytes and reticulocytes prelabelled with 32P-Pi revealed a high turnover of the monoester phosphate groups of PIP2 in reticulocytes, which declines strongly during maturation [Maretzki et al., Biomed. Biochim. Acta 45, 1227-1236 (1986)]. The 3H-inositol uptake exhibits a strong maturational loss. A carrier-mediated uptake of inositol in reticulocytes is suggested. In reticulocytes PI, PIP and PIP2 incorporated 3H-inositol in the relative distribution of 86; 5 and 9%, respectively, but only PI to a minor extent in erythrocytes. A small release of 3H-labelled inositol phosphates was found in reticulocytes, which was not stimulated by extracellular calcium during incubation. Determination of the 32P/3H-ratio in double-labelled phosphatidylinositides in reticulocytes demonstrated a very slow turnover of the diester phosphate bonds compared with that of the inositol phosphate ester groups.

Animals↗
PubMed1986

Maturation of rabbit reticulocytes: strong decline of the turnover of polyphosphoinositides.

The [32P]phosphate labelling of ATP and polyphosphoinositides (PI) of intact rabbit reticulocytes and mature erythrocytes was compared. Despite the fact that reticulocytes have a 30-fold higher turnover of ATP than mature erythrocytes, the 32P-labelling of the cellular ATP pool was identical. The 32P-Pi entry into the cells is the rate-limiting step for 32P-phosphate isotopic equilibration of the ATP-pool and is independent of maturation. The rates of 32P-phosphate incorporation into PI-4,5-P2 and into PI-4-P, respectively, were 17-fold and 8-fold higher in reticulocyte-rich cell suspensions than in erythrocytes. The specific radioactivity of PI-4,5-P2 labelling reaches 55% and that of PI-4-P 40% of the ATP specific activity. However, a rapid isotopic equilibration of the polyphosphoinositides, was found. These findings indicate the existence of a heterogeneity of polyphosphoinositide pools. Reticulocyte membranes lose about 30% of their polyphosphoinositides during maturation proportional to the total loss of phospholipids.

Adenosine Triphosphate↗
PubMed1983

[Anastomoses between the segmental arteries of the liver and phrenicohepatic arterio-arterial anastomoses].

A corrosion - cast anatomical study was performed on human livers. At first arterio-arterial anastomoses between the inferior phrenic arteries and branches of the main hepatic artery were investigated. Secondly, arterial communications between the right and left hepatic artery are described. 1. The anatomical-functional study of phrenico-hepatic anastomoses gives new detailed information on the arterial blood supply of the liver out of the phrenic arteries. These collaterals are a consistent finding. By far the largest part of the phrenicohepatic anastomoses is derived from the right inferior phrenic artery. The superior and posterior segments receive most of the anastomoses. In about 10% of our cases we succeeded in filling almost the whole arterial system of the liver by injecting the inferior phrenic arteries. 2. There are three anastomotic pathways from the right hepatic artery to the left: the so-called portal anastomoses (hilar anastomoses), translobar vessels, and the capsular arteries.

Adult↗
PubMed1981

ATP utilizing reactions of human erythrocyte membranes and the influence of modulator proteins.

The ATP production of human erythrocytes in the steady state (approximately 2 mmoles . 1 cells-1 . h-1, 37 degrees C, pHi 7.2) is maintained by glycolysis and the ATP consumption is essentially limited to the cell membrane. About 25% of the ATP consumption is used for ion transport ATPases. The bulk of the ATP consuming processes in intact erythrocytes remains poorly understood. "Isotonic" erythrocyte membranes prepared under approximate intracellular conditions after freeze-thaw hemolysis have high (Ca2+, Mg2+)-ATPase activities (80% of the total membrane ATPase activity). There is a great discrepancy between the high capacity of the (Ca2+, Mg2+)-ATPase in isotonic membranes and the actual activity in the intact cell. The (Ca2+, Mg2+)-ATPase of isotonic membranes has a "high" Ca2+-affinity (Ka less than 0.5 microM) and a "low" Mg-ATP affinity (Km approximately 760 microM). This state of (Ca2+, Mg2+)-ATPase is caused by the association of calmodulin and 30000 Dalton polypeptides (ATP affinity modulator protein). Hypotonic washings of isotonic membranes result in a loss of the 30 kD polypeptides. EGTA (0.5 mM) extracts derived from isotonic membranes contain the 30 kD modulator protein and restore the properties of the (Ca2+, Mg2+)-ATPase of hypotonic membrane preparations to the isotonic characteristics. The Mg-ATP affinity modulator protein is assumed to form a complex with calmodulin and (Ca2+, Mg2+)-ATPase.

Adenosine Triphosphate↗
PubMed1981

Membrane phosphorylation in intact human erythrocytes.

The time course of 32P incorporation into ATP and monoesterified membrane phosphatases was studied within 1 h of incubation of intact human erythrocytes. Analysis of membrane proteins and phospholipids showed dynamically exchanged phosphates mainly in the phospholipid fraction. The extent of ATP turnover by spectrin band 2 polypeptide phosphorylation was very small. The 32P-ATP and the membrane 32P-phosphate label could be chased via the metabolism by the addition of extracellular Pi. From the relative changes in the specific radioactivity of ATP and of the membrane phosphate in intact erythrocytes we assume that about 60% of the erythrocyte ATP production are linked to the ATP consumption by the rapid polyphosphoinositide turnover. It is conceivable that there is a connection between the protein factors modifying the affinity of (Ca2+, Mg2+)-ATPase and the metabolism of the polyphosphoinositides in the erythrocyte membrane.

Adenosine Triphosphate↗
PubMed1979

Early molecular events in the interaction of enveloped viruses with cells. I. A fluorescence and radioactivity study.

The fluorescence depolarization of 1,6-diphenyl-hexatriene was used to study the dynamic properties of the hydrophobic regions of the lipid envelopes of ortho- and paramyxoviruses as well as of the Rous sarcoma virus and of the membrane lipids of susceptible and nonsusceptible cells. The systems investigated where active and inactive influenza viruses, and NDV virus acting on chick embryo fibroblasts and Rous sarcoma virus acting on susceptible (C/E) and nonsusceptible (C/B) chicken-cell. Polarization degrees and mean rotational correlation times of DPH embedded in viral lipids were significantly higher than those of DPH in the cell membranes, due to a higher rigidity of the virus envelopes. When suspensions of labelled viruses and unlabelled cells or unlabelled viruses and labelled cells were mixed, a characteristic change of the fluorescence polarization degrees with time was observed. This behaviour was ascribed to label transfer from virus to cell membranes or vice versa. While the rate constants of label transfer from virus to cells and cells to virus were about the same for the penetrating viruses the rate constants of label release from inactive virus to cells were much larger than for the migration in the opposite direction.

Animals↗
PubMed1979

Early molecular events during the interaction of enveloped riboviruses with cells. II. A kinetic study.

A kinetic model was constructed and partly solved to describe the migration of the fluorescence label 1,6-diphenylhexatriene (DPH) in both directions when enveloped viruses, labelled with DPH in their envelopes are in contact with unlabelled cells or cell labelled in their membranes are in contact with unlabelled enveloped viruses. The central assumption is that two types of receptor sites exist on the cell surface, i.e., physical adsorption sites (P-sites), available to all the viruses studied in these papers and binding sites (B-sites) available only to the viruses which penetrate into the specific cells. The differential equations for the label migration, for different values of the ratio number of viruses number of sites were numerically solved, assuming different fractions of P- and B-sites. The equations also describe, appropriately the mechanism of rapid label migration in the system and substantiate the magnitude "time of residence" of the nonpenetrating viruses adsorbed on the cell surface. The resulting curves match satisfactorily those for the label release by the viruses and account well for the steady state values of the kinetics of label migration in the virus-cell system.

Adsorption↗
PubMed1975

[Control intensity of glycolytic enzymes in ultrasonic hemolysates of erythrocytes].

By addition of enzyme the control intensity was determined on the pacemaker enzymes hexokinase and phosphofructokinase, as well as on glyceraldehyde-3-phosphate-dehydrogenase and the pyruvate kinase with a control intensity of almost 0 in ultrasonic hemolysates from erythrocyte concentrate. This hemolysate approximately reflects the conditions existing in the intact cell with regard to glycolytic rate, ATP supply, and metabolite concentration. It is therefore suitable as a cell model, excluding the membrane, for studying inner control factors. For HK, PFK, GAPD, and PK predictions based on the linear glycolytic model about the significance of these enzymes for the regulation of the glycolytic rate could be confirmed.

Erythrocytes↗