Inhibition of creatine kinase by iodoalkanes. Further appraisal of the essential nature of the reactive thiol group.

Creating kinase (ATP: creatine N-phosphotransferase) is completely inhibited by low molecular weight iodoalkanes in a pseudo first order reaction. Analysis of this and other data suggests that covalent modification per se is not a sufficient criterion to establish whether or not an enzyme group is essential for catalysis.     

Protein--immobilized lipid in dimyristoylphosphatidylcholine-substituted cytochrome oxidase: evidence for both boundary and trapped-bilayer lipid.

Cytochrome oxidase-dimyristoyl phosphatidylcholine complexes have been prepared at defined lipid:protein ratios to study the effects of protein packing density on the lipid fluidity. All the complexes reveal a two-component ESR spectrum from an incorporated phosphatidylcholine spin label, corresponding to both an immobilized lipid boundary layer and fluid bilayer regions. Difference spectra, obtained by subtracting the same immobilized spectrum from the spectra of the various complexes, demonstrate a strong perturbation of the lipid bilayer fluidity which is quite distinct from the immobilized boundary layer formation.     

Ecological studies on Indonesian lakes. Overturn and restratification of Ranu Lamongan

In July 1974 Ranu Lamongan overturned. The resulting deoxygenation of this small tropical crater lake killed some of its fishes. This paper describes the recovery of stratification of temperature and oxygen and follows short-term changes in the plankton during the three weeks after overturn. The lake is fringed with a floating mat of Eichhornia whose submerged roots support and shelter a rich community of invertebrates on which much of the fishery depends. Comparison of our findings with those of the German Sunda Expedition in 1928 show remarkably few changes in the lake or its biota during the 45-year interval, despite a marked increase in the human population and the introduction of four species of fishes.     

Phospholipase A2 as a probe of phospholipid distribution in erythrocyte membranes. Factors influencing the apparent specificity of the reaction.

The action of snake venom phospholipases A2 in intact human erythrocytes was investigated in detail. The basis phospholipase from Agkistrodon halys blomhifii was found to induce both hydrolysis of membrane phospholipids and total cell hemolysis under certain experimental conditions. The hydrolytic action of the basic enzyme was found to consist of two sequential events: (a) hydrolysis of 70% of the total cell ph osphatidylcholine without any evident hemolysis; and (b) complete hydrolysis of the remaining phosphatidylcholine, followed closely by extensive phosphatidylethanolamine hydrolysis and finally with onset of hemolysis, attack on the phosphatidylserine. At pH 7.4 and 10 mM Ca2+ only stage (a) occurred. However, a slight elevation of the pH of incubation to pH 8.0 and/or inclusion of 40 mM Ca2+ in the reaction mixture caused both events (a) and (b) to occur. The addition of glucose limited the action of the enzyme to stage (a) under any reaction conditions. An investigation showed that enzymically induced hemolysis occurred under conditions where the intracellular ATP levels were lowered. Data are presented which suggest that stage (b) is mediated by in influx of Ca2+ into the cell when the levels of ATP are low. Interestingly the phosphllipase from Naja naja venom (Pakistan) yielded results similar to those observed with the basic enzyme from Agkistrodon venom. However, the enzyme from Crotalus adamanteus and the acidic enzyme also present in the Agkistrodon venom produced only slight hydrolysis or hemolysis under any of the conditions studied. Other species of erythrocytes, e.g., guinea pig, monkey, pig, and rat, were tested but only those from guinea pig behaved similarly to the human cells. Pig, monkey, and rat erythrocytes underwent very limited hydrolysis and hemolysis. It is evident that the use of these phospholipases to probe the localization of phospholipds in erythrocyte membranes must be approached with caution. Certain facets of this problem are discussed.     

Air and soil temperature differences in controlled environments,as a consequence of high radiant flux densities and of day/night temperature changes

Summary Soil/air temperature differences were measured in 15 cm diameter plastic pots and in 30-cm diameter fibre pots under high radiant flux densities in a controlled environment cabinet. When there was no surface insulation or shading on the sides of the plastic pots, soil temperatures at –1 cm equilibrated at 7.5°C above air temperature. Reflective surface covering and shading on the sides of the pot reduced this difference to 2.4°C. In the fibre pots with reflective surface covering and side shading, soil equilibrium temperature was 1°C below air temperature, but equilibration time was 8 to 9 hours following day/night temperature changes.