Colchicine resistant friend cells: Application to the study of actinomycin D induced erythroid differentiation

Colchicine resistant (Cch^R) mutants have been isolated from Friend erythroeleukemic cells by successive single-step selections. Measurements of the rate of uptake of [³H]-colchicine into whole cells, and the binding of [³H]-colchicine to cytoplasmic extracts, suggest that these mutants are colchicine-resistant due to a reduced membrane permeability to colchicine, rather than an altered intracellular colchicine-binding target. Consistent with this conclusion is the observation that non-toxic concentrations of Tween–80, a non-ionic detergent, potentiated colchicine uptake into mutant cells. In addition, these Friend cell mutants, like Cch^R mutants of other cell types, are cross-resistant to a variety of unrelated drugs, including daunomycin, puromycin, emetine, and actinomycin D. A comparison of the dose-response curves for the induction of Friend cell differentiation by actinomycin D of both wild-type and two Cch^R cells suggests that actinomycin D permeation is required for its effects on Friend cell differentiation. Potentiation of actinomycin D uptake by Tween–80 significantly lowered the concentration of drug required to induce hemoglobin synthesis in the Cch^R cells, but had no significant effect on either actinomycin D induction of Cch^S cells or DMSO induction of both Cch^S and Cch^R cells. In common with other chemical inducers of Friend cell differentiation, the addition of actinomycin D results in an early decrease in ⁸⁶ RbCl uptake, although this effect on transport occurred 14 hours later than that observed with DMSO.     

Comments on ''Reaction mechanism of flavin-dependent hydroxylation: evolution of a non-imitable enzyme'' by C. M. Visser. Research note on the possible occurrence of dioxetanes and other cyclic peroxides in flavin and pteridine-mediated hydroxylations

A new method of purification of chloroplastic thioredoxins has been presented. This method is based on affinity chromatography on fructose-bisphosphatase--Sepharose columns. Two thioredoxin, fA and fB, may be extracted and purified to homogeneity from the same leaf extract. Whereas fA is monomeric and has an Mr of 11 400 +/- 500, fB is dimeric with an Mr of 18 000 +/- 600. The dimer dissociates in two halves in the ultracentrifuge under the effect of high pressures. Raising the ionic strength results in the same effect. Thioredoxins fA and fB activate to similar extents chloroplastic fructose bisphosphatase and NADP--malate dehydrogenase. Chloroplastic sedoheptulose bisphosphatase is activated by thioredoxin fB but not by thioredoxin fA.     

Use of a rapid ultrafiltration technique in the determination of plasma glycerol

The use of plasma ultrafiltrates in the enzymatic analysis of glycerol has been compared with filtrates prepared by using metaphosphoric acid and heat denaturation. The results which were obtained with these three methods of deproteinization are comparable; however, the membrane ultrafiltration technique is the simplest of the procedures and yields an undiluted filtrate which is free of foreign ions.     

Further developments in the breeding population of lowland gorillas at Apenheul

In 1987 a second group of lowland gorillas was formed at Apenheul. Aspects of the zoo-technical management (diet, accommodation, etc.) are described. The management and the development of the population, including mother-rearing of all offspring, are described. Special attention is given to the formation of a second group by introducing two zoo-born females and a non-breeding female from one group to a nonrelated male to form a second group. These transfers of group members resulted rather quickly in pregnancies. The two groups are housed on adjacent islands, and the advantages and disadvantages of such a facility are discussed.