VARIATION IN THE DURATION OF MITOSIS IN THE CRYPTS OF LIEBERKUHN OF THE RAT; A CYTOKINETIC STUDY USING VINCRISTINE

The variation in the duration of mitosis ( t _m) with cell position in the small intestinal crypts of the adult rat has been measured by a stathmokinetic technique using vincristine. The value for the whole crypt column was 0.43 hr, or 26 min. At the bottom of the crypt t _m was in excess of 1 hr, but rapidly decreased and throughout the greater part of the proliferative compartment was between 0.40 and 0.50 hr. At the top of the proliferative compartment an increase in t _m was demonstrated.
If the value of 0.43 hr for the whole crypt column is correct, then one argument for postulating the formation of metabolic DNA during differentiation in the small bowel epithelium of the rat becomes invalid. Variations in t _m within the crypt have been shown to increase the values of cell velocity obtained from cumulative birth rate diagrams. Finally further evidence has been presented for the existence of a slowly dividing subpopulation of cells at the base of the crypt. These cells may be important in crypt repopulation after damage with phase specific anti-tumour drugs.     

Certain organism-substrate relationships affecting the distribution of Uca minax (Crustacea: Decapoda)

The involvement of substrate in the ecology of the fiddler crab Uca minax was investigated by means of both field and laboratory studies. These included determination of the oxygen-holding capacities of five types of substrates on which this organism lives, as well as experiments to determine if there is substrate selection. The effect of population density on burrowing was also studied to determine the optimum number of individuals needed in the selection experiments, and to delineate the mechanisms these organisms use for avoiding dispersion onto less favorable substrates. Results indicate that Uca minax prefers substrates with high organic content, although these were shown to contain the lowest substrate oxygen. This evidence suggests that Uca minax prefers substrates of high energy value, and explains the significance of this species' adaptation in withstanding low oxygen tensions. Population density experiments indicate that at high population densities these crabs reduce intraspecific encounter and competition by burrowing and subsequently covering their burrows. Seasonal monitoring of burrow temperatures indicate the stability of this microenvironment as compared with the surrounding air temperature. These data also demonstrate the significance of the adjacent water in the habitat ecology of Uca minax.     

Cholinesterase in larvae of the ascidian,Ciona intestinalis,developing from fragments cut from centrifuged eggs

Development Genes and Evolution - UnfertilizedCiona eggs were centrifuged, stratifying their mitochondria and some other cytoplasmic components. Each centrifuged egg had a mitochondria-free,...     

The action of local anaesthetics on lipolysis and on adenosine 3′:5′-cyclic monophosphate content in isolated rat fat-cells

1. Local anaesthetics inhibited hormone-stimulated lipolysis in isolated rat fat-cells. The most potent anaesthetic was dibucaine, which inhibited adrenaline-stimulated lipolysis by 50% at a concentration of 0.16mm. 2. The amount of inhibition produced by a given concentration of anaesthetic was very similar with adrenaline, theophylline and dibutyryl cyclic AMP, at submaximal and maximal concentrations. 3. The inhibitory effect of dibucaine on lipolysis was apparent within 5 min and was constant over 1h. 4. Dibucaine inhibited basal, adrenaline-stimulated and insulin-stimulated glucose uptake at concentrations 6-10-fold higher than those inhibiting lipolysis. 5. The effects of dibucaine on lipolysis and glucose uptake were reversed after removal of anaesthetic and washing of cells. 6. Dibucaine further elevated the concentration of cyclic AMP in the presence of adrenaline or adrenaline plus theophylline. 7. Dibucaine had no effect on ATP content at concentrations causing 80% inhibition of lipolysis, but lowered ATP content at higher concentrations. 8. The relative potency of different local anaesthetics as inhibitors of hormone-stimulated lipolysis paralleled their potency as inhibitors of ion movements in other systems. 9. The possibility is discussed that Ca(2+) ions are involved in the regulation of lipolysis, and that local anaesthetics inhibit lipolysis by interfering with Ca(2+) translocation.     

Nitrite oxidase and nitrate reductase in Nitrobacter agilis

Nitrite oxidase and nitrate reductase in Nitrobacter agilis were shown to be separate enzymes. The best separation of the two systems was achieved by ammonium sulphate fractionation. The effects of various compounds, including antimycin A, 2-n-heptyl-4-hydroxyquinoline N-oxide and chlorate, also clearly distinguish between the two enzyme reactions. The relationship between the two opposing reactions in Nitrobacter is discussed.     

A nitrite reductase with cytochrome oxidase activity from Micrococcus denitrificans

The formation of nitrite reductase and cytochrome c in Micrococcus denitrificans was repressed by O₂. The purified nitrite reductase utilized reduced forms of cytochrome c, phenazine methosulphate, benzyl viologen and methyl viologen, respectively, as electron donors. The enzyme was inhibited by KCN, NaN₃ and NH₂OH each at 1 mM, whereas CO and bathocuproin, diethyl dithiocarbamate, o-phenanthroline and ,'-dipyridyl at 1 mM concentrations were relatively ineffective. The purified enzyme contains cytochromes, probably of the c and a₂ types, in one complex. A K_m of 46 μM for NO₂⁻ and a pH optimum of 6.7 were recorded for the enzyme. The molecular weight of the enzyme was estimated to be around 130000, and its anodic mobility was 6.8·10⁻⁶ cm²·sec⁻¹·V⁻¹ at pH 4.55.

The most highly purified nitrite reductase still exhibited cytochrome c oxidase activity with a K_m of 27 μM for O₂. This activity was also inhibited by KCN, NaN₃ and NH₂OH and by NO₂⁻.

A constitutive cytochrome oxidase associated with membranes was also isolated from cells grown anaerobically with NO₂⁻. It was inhibited by smaller amounts of KCN, NaN₃ and NH₂OH than the cytochrome oxidase activity of the nitrite reductase enzyme and also differed in having a pH optimum of about 8 and a K_m for O₂ of less than 0.1 μM. Spectroscopically, cytochromes b and c were found to be associated with the constitutive oxidase in the particulate preparation. Its activity was also inhibited by NO₂⁻.

The physiological role of the cytochrome oxidase activity associated with the purified nitrite reductase is likely to be of secondary importance for the following reasons: (a) it accounts for less than 10% of total cytochrome c oxidase activity of cell extracts; (b) the constitutive cytochrome c oxidase has a smaller K_m for O₂ and would therefore be expected to function more efficiently especially at low concentrations of O₂.     

Studies on the incorporation of labelled sulphate into cells and cell-free extracts of Nitrosomonas europaea

Summary The incorporation of [³⁵S]sulphate was followed into the washed cell suspensions of Nitrosomonas europaea. Thus bound sulphate, sulphite, sulphide, cysteine, glutathione, homocysteine and methionine were found in the ethanol soluble fraction as well as in the residual hydrolysed protein fraction. Cysteic acid, methionine sulphoxide and methionine sulphone were detected in the residual protein. The reaction between sulphydryl groups and N-ethylmaleimide has been successfully used to stabilize the thiol compounds in cell-extracts and the derivatives thus obtained were separated by paper chromatography. As in other microorganisms, sulphate is first activated by ATP in Nitrosomonas before it is reduced. The formation of APS and PAPS has been studied. A pathway for the incorporation of [³⁵S]sulphate is proposed.Abbreviations POPOP 1,4-bis-(5-phenyloxazolyl-2)-benzene - PPO 2,5-diphenyloxazole - APS adenosine-5-phosphosulphate - PAPS adenosine-3-phosphate 5-phosphosulphate - ATP adenosine triphosphate - DNA-ase deoxyribonuclease - NEM N-ethylmaleimide - TCA trichloro-acetic acid - GSH glutathione