Peter H. Lowy

Response of Normal and Genetically Anaemic Mice to Erythropoietic Stimuli

results in a lifelong macrocytic anaemia (Russell, 195.5, 1962). Gene action leading to thc liacmatopoietic defect of WWv animals is known to occur in the haernatopoietic cells themselves, rather than being imposed from another part of the body. This has been demonstrated repeatedly by successful implantation of haematopoietic cells froin normal tvzv foctal liver into adult and juvenile WWv anaemic mice (Russell, Smith and Lawson, 1956; Bernstein and Russell, 1959). The implanted cells function autonomously according to their own wzv gcnotypc, and thc blood picture of the host changcs gradually but pcrmanently to tha t of a normal mouse. In the present experiments four types of adult mice were used: sevcrcly anaemic WWv mice ; haematologically nornial ww and Ww mice ; very slightly aiiaeniic WUzv inice ; and chimaeric individuals whose original genotype was WWv but which had acquired a lloriiial wtu blood picture following implantation of isologous ww hacmatopoictic cells. An erythropoictic hormone, erythropoictin (EP), niay be obtained from sevcrely aiiacniic animals, for instance froin the plasma or rabbits or sheep made anaemic by blccdiiig or by phenylhydrazinc-induced hacmolysis. It is also found in the urine of some anaeniic aninials

Polypeptides Minimine and Melittin from Bee Venom: Effects on Drosophila

Abstract Bee venom was fractionated using methanol, acetone, polyacrylamide, and Sephadex gels, and anion exchangers. Two polypeptides were isolated and found to have unique physiological effects on Drosophila melanogaster larvae. One of these—minimine—has a molecular weight of about 6000, contains all of the usual amino acids, and has not been previously described. Third-instar larvae which survive the LD 50 dose of about 0.005 μg of minimine stop feeding and growing and are lethargic but not paralyzed. They develop into flies as small as one-fourth of normal but normal with regard to feeding and mobility. These reproduce, and their progeny are of normal size at the larval and adult stages. The main component of bee venom—melittin—was isolated in two very similar forms. Its in vivo physiological and in vitro anti acetylcholinesterase effects are described in the accompanying paper.

Melittin: toxicity to Drosophila and inhibition of acetylcholinesterase

Abstract The bee venom peptide melittin has been found to be highly toxic in vivo to Drosophila larvae. It is also a noncompetitive inhibitor of acetylcholinesterase. In both cases the cations Na + , K + , and Mg 2+ are strongly antagonistic to the effects of the peptide. It appears that the toxicity of melittin is due to membrane disruption, with a differential sensitivity among different cell types although inhibition of acetylcholinesterase may also be involved.

Stimulation by Serotonin of Erythropoietin‐dependent Erythropoiesis in Mice

Summary. Serotonin stimulates erythropoiesis in normal mice but not in the presence of anti‐erythropoietin serum. It also stimulates erythropoiesis in adrenalectomized or hypophysectomized mice. It increases erythropoietin titres in the plasma of normal but not of nephrectomized mice. The serotonin precursor l‐5‐hydroxytryptophan stimulates, but d‐5‐hydroxytryptophan and the serotonin catabolite 5‐hydroxyindoleacetic acid do not.

Inactivation of erythropoietin by Koshland's tryptophan reagent and by membrane filtration

Abstract 1. 1. Reaction with 2-hydroxy-5-nitrobenzylbromide ( Koshland s reagent) inactivates human and rabbit erythropoietin. Fifteen amino acids and two hexosamines are found unchanged but most of the tryptophan is missing in the reacted erythropoietin. It is probable that one or more intact tryptophan moieties are obligatory for the biological activity. 2. 2. There are great losses when mg quantities of erythropoietin are filtered through Millipore membranes. Protein relatively rich in tryptophan along with the activity appears to be selectively held on the membrane. Selas Flotronics membranes (made of silver) cause almost no loss of activity and are therefore preferable for sterilization of small amounts of erythropoietin, as in cell culture experiments. 3. 3. Human urinary erythropoietin reacts with anti-human albumin serum but differs from albumin by carbohydrate components (hexoses, hexosamines and sialic acid) linked to the protein. Since the tryptophan content of the erythropoietin is higher than that of albumin the immunological reaction cannot be due to albumin which by linkage with carbohydrates has acquired erythropoietin character.

Question of Purity of Erythropoietic Factor Concentrates.

Summary The bulk of erythropoietic activity of anemic plasma can be concentrated in a fraction which represents less than 0.5% of plasma proteins. Yet from the similarity in yield and electrophoretic behavior of the corresponding inactive fraction from normal plasma, it appears likely that the erythropoietic factor constitutes only a small portion of the present concentrates.

Bee venom phospholipase A2; effects on Drosophila larvae, HeLa cells and membranes.

Abstract P. H. Lowy , H. K. Mitchell and U. W. Tracy . Bee venom phospholipase A 2 : effects on Drosophila larvae, HeLa cells and membranes. Toxicon 14, 203–212, 1976.— Drosophila larvae injected with sublethal doses of bee venom phospholipase A 2 become lethargic, stop feeding and growing, but undergo metamorphosis and emerge as miniature flies which give rise to normal progeny. One-third of the electrophoretically homogeneous enzyme binds more strongly than the rest to membranes from larval tissue. The enzyme increases the permeability of the inner membrance of pigeon heart mitochondria, allowing passage of neutral molecules at least as large as tetrasaccharide. Electron microscope evidence shows a concentration-dependent swelling short of actual membrane disruption even at very high enzyme concentrations. The enzyme does not affect erythrocytes but causes the appearance of many lipid droplets in the cytoplasm of HeLa cells. The peculiar starvation-like effect of phospholipase A 2 on larvae may result from leakage due to conformational changes in membranes rather than extensive hydrolysis of membrane phospholipid.