Induction, differentiation and oncogenesis

Eukaroytic cytodifferentiation usually leads to stable end-states. However, evidence on embryonic induction in amphibia supports the view that the initial stages of cellular maturation following induction of differentiation are comparatively labile, stability being a property acquired during maturation.Early developing cells may therefore retain the capacity for reversion to their previous, less developed, condition and a proportion of any group of induced cells may do so. Possible implications of such a phenomenon are explored, using two kinetic models of reversion. It is concluded that reversion is a possible mechanism in leukaemogenesis and other forms of oncogenesis.     

The Stoichiometry of Respiration-driven Potassium Transport in Corn Mitochondria

Determinations were made for corn (Zea mays L., WF9-Tms × M14) mitochondria of the stoichiometric relationship between K⁺ transport and bond energy produced in respiration (K⁺/~ ratio). With inward pumping of potassium acetate activated by NADH oxidation, the initial rate of K⁺ transported into the sucrose inaccessible space varied between 0.58 and 0.97 K⁺/~, assuming 2 high energy bond equivalents per NADH oxidized. Only small amounts of H⁺ were ejected. Valinomycin did not alter the ratio.     

Photosystem II regulation of macromolecule synthesis in the blue-green alga Aphanocapsa 6714.

Polymers synthesized by heterotrophically growing (glucose as carbon source) cultures of Aphanocapsa 6714 were compared with polymers synthesized in photosynthetically grown cultures. Loss of photosystem II by dark incubation, or inhibition of light-grown cells with the photosystem II-specific inhibitor dichlorophenylmethylurea, caused an 80 to 90% reduction in the rate of lipid and total ribonucleic acid synthesis, and more than a 90% reduction in the rate of protein synthesis. In contrast, glycogen synthesis was reduced only about 50% in dark cells and less than 30% in dichlorphenylmethylurea-inhibited cells. After longer heterotrophic growth, glycogen became the major component, whereas in photosynthetically grown cultures protein was the major constituent. 14C (from 14CO2 and/or [14C]glucose) assimilated into protein by heterotrophically grown cells was found in amino acids in nearly the same proportions as in photosynthetically grown cells. Thus, routes of biosynthesis available to autotropic cells were also available to heterotrophic cultures, but the supply of carbon precursors to those pathways was greatly reduced. The limited biosynthesis in heterotrophic cells was not due to a limitation for cellular energy. The adenylates were maintained at nearly the same concentrations (and hence the energy charge also) as in photosynthetic cells. The concentration of reduced nicotinamide adenine dinucleotide phosphate was higher in heterotrophic (dark) cells than in photosynthetic cells. From rates of CO2 fixation and/or glycogen biosynthesis it was determined that stationary-phase cells expended approximately 835, 165, and less than 42 nmol of adenosine 5'-triphosphate per mg (dry weight) of algae per 30 min during photosynthetic, photoheterotrophic, and chemoheterotrophic metabolism, respectively. Analysis of the soluble metabolite pools in dark heterotrophic cultures by double-labeling experiments revealed rapid equilibration of 14C through the monophosphate pools, but much slower movement of label into the diphosphate pools of fructose-1,6-diphosphate and sedoheptulose-1,7-diphosphate. Carbon did flow into 3-phosphoglycerate in the dark; however, the initial rate was low and the concentration of this metabolite soon fell to an undetectable level. In photosynthetic cells, 14C quickly equilibrated throughout all the intermediates of the reductive pentose cycle, in particular, into 3-phosphoglycerate. Analysis of glucose-6-phosphate dehydrogenase in cell extracts showed that the enzyme was very sensitive to product inhibition by reduced nicotinamide adenine dinucleotide.     

Pulmonary angiotensin-converting enzyme. Interspecies homology and inhibition by heterologous antibody in vivo.

Goat antibody against pure rabbit pulmonary angiotensin-converting enzyme was used to probe homology of converting enzymes from other species. Immunologically cross-reactive material was found in detergent-solubilized extracts of lung particles from rat, guinea pig, and dog by double immunodiffusion, radioimmunoassay, and inhibition of enzyme activity. No homology was demonstrable with bovine, frog, or chicken lung extracts. Antibodies from different individual goats yielded comparable estimates of homology by immunodiffusion and radioimmunoassay. In contrast, they varied greatly in extent and specificity of their inhibitory action on heterologous enzyme activity. The vasopressor effect of angiotensin I and the vasodepressor effect of bradykinin were diminished and potentiated, respectively, in rats treated with anti-rabbit enzyme antibody. A smaller but significant immune-dependent inhibition of the vasopressor response to angiotensin II was also observed.     

A synthesis of 7α-hydroxyandrost-4-ene-3, 17-dione

The first convenient chemical synthesis of 7α-hydroxyandrost-4-ene-3,17-dione is reported. Androsta-4,6-diene-3,17-dione was converted into its 6α,7α-epoxy-derivative; reduction of the epoxide with aluminium amalgam gave 7α-hydroxyandrost-4-ene-3,17-dione. This reducing agent is more efficient than chromous acetate for the purpose.     

Anion transport and membrane morphology

Summary Freeze-fracture electronmicroscopy has been used to examine the membrane ultrastructure of human red blood cells in the presence of inhibitors of chloride exchange. The extent of inhibition was correlated with a decrease of intramembrane particle density on the B-fracture face. Dimethylsulfoxide (DMSO) and glycerol, which markedly and reversibly reduced the intramembrane particle density, were shown to drastically and reversibly inhibit chloride self-exchange. DMSO was shown to be a noncompetitive inhibitor of chloride flux.     

Fungal degradation of kraft lignin and lignin sulfonates prepared form synthetic 14C-lignins

Kraft lignins (KL), bleached kraft lignins (BKL), and lignin sulfonates (LS) were prepared from synthetic ¹⁴C-lignins labeled in the aromatic nuclei or in the propyl side chains. These and control lignins (CL) were incubated with the lignin-decomposing white-rot fungus, Phanerochaete chrysosporium Burds., in a defined culture medium containing cellulose as growth substrate. Decomposition was monitored by measuring the ¹⁴CO₂ evolved. Average percentages of the [ring-¹⁴C]- and [side chain-¹⁴C]-lignins, respectively, recovered as ¹⁴CO₂ at the cessation of ¹⁴CO₂ evolution were: KL, 41 and 31; BKL, 42 and 26; LS, 28 and 21; and CL, 26 and 24. Gel permeation chromatography of radiolabeled materials extracted from spent cultures showed that substantial degradation to nonvolatile products had occurred. The polymeric components in the extracts were further degraded in fresh cultures. These results indicate that industrial lignins are significantly bioalterable, and that under favorable conditions industrial lignins are substantially biodegradable.     

SYNTHETIC STRANDS OF CARDIAC MUSCLE : Formation and Ultrastructure

Spontaneously active bundles of cardiac muscle (synthetic strands) were prepared from isolated cells of 11–13-day old embryonic chick hearts which were disaggregated with trypsin. Linear orientation of the cells was obtained by plating them on agar-coated culture dishes in which either grooves were cut in the agar film or a thin line of palladium was deposited over the agar. The influence of cell-to-cell and cell-to-substrate interactions was observed with time lapse cinematography and the formation of the synthetic strand was shown to involve both random and guided cell movements, enlargement of aggregates by accretion and coalescence, and the compact linear arrangement of cells along paths of preferential adhesion. Electron microscope investigations of these strands showed that a dispersed population of heart cells organized into an inner core of muscle cells and an outer sheath of fibroblast-like cells. The muscle cells contained well-developed, but widely spaced myofibrils, a developing sarcoplasmic reticulum associated in part with the myofibrils and in part with the sarcolemma, an abundance of nonmembrane bound ribosomes and glycogen, and a prominent Golgi complex. Numerous specialized contacts were observed between the muscle cells in the strand, e.g., fasciae adherentes, desmosomes, and nexuses. A distinct type of muscle cell characterized by its pale appearance was regularly observed in the strand and was noted to be similar to Purkinje cells described in the adult avian conduction system and in developing chick myocardium. The present findings were compared with other observations of the developing myocardium, in situ, and it was concluded that, by a number or criteria, the muscle cells of the strand were differentiating normally and suitably organized for electrophysiological studies.     

A conditional-lethal molybdopterin-defective mutant of barley

Summary The molybdenum cofactor of the barley mutant R9401 is not able to reconstitute NADPH nitrate reductase activity from extracts of the N. crassa nit-1 mutant nor is it able to effect dimerisation of the nitrate reductase subunits present in the R9401 mutant. Unphysiologically high levels of molybdate cannot restore nitrate reductase and xanthine dehydrogenase activity to mutant R9401 in vivo nor reactivate the Mo-co factor in vitro. The results indicate that the defect in mutant R9401 lies in the pathway leading to the formation of a functional molybdopterin moiety and that the same nuclear gene is involved in the synthesis of both shoot and root molybdenum cofactor.Abbreviations BSA bovine serum albumen - GSH glutathione (reduced) - NEM N-ethylmaleimide