Metabolic rate, maximum metabolism, and advantages of torpor in the fat mouse Steatomys pratensis natalensis Roberts, 1921 (Dendeomurinae)

1. The fat mouse Steatomys pratensis natalensis (mean body mass 37.4±0.43 (se)) has a low euthermic body temperature T_b=30.1–33.8 °C and a low basal metabolic rate (BMR)=0.50 ml O₂ g⁻¹ h⁻¹.

2. Below an ambient temperature (T_a)=15 °C, the mice were hypothermic.

3. The lowest survivable T_a=10 °C.

4. Torpor is efficient in conserving energy between T_a=15–30 °C, below T_a=15 °C, the mice arouse.

5. Euthermic and torpid mice were hyperthermic at T_a=35 °C.

6. Thermal conductance was 0.159 ml O₂ g⁻¹ h⁻¹ °C⁻¹, 98.8% of the expected value.

7. Non-shivering thermogenesis (NST) was 2.196 ml O² g⁻¹ h⁻¹ (3.69×BMR).

8. Maximal oxygen consumption, however, was 3.83 ml O₂ g⁻¹ h⁻¹ (6.44×BMR), indicating that other methods of heat production are additive.

9. Because fat mice conserve energy by torpor only between T_a=15–30 °C, we suggest that torpor may be a more important mechanism for surviving food shortages than for surviving cold weather.

Evidence of multiple operational affinities for d-glucose inside the human erythrocyte membrane

1. 1. The Michaelis-Menten parameters of labelled d-glucose exit from human erythrocytes at 2°C into external solution containing 50 mM d-galactose were obtained. The K_m is 3.4 ± 0.4 mM, V 17.3 ± 1.4 mmol · 1⁻¹ cell water · min⁻¹ for this infinite-trans exit procedure.

2. 2. The kinetic parameters of equilibrium exchange of d-glucose at 2°C are K_m = 25 ± 3.4 mM, V 30 ± 4.1 mmol · 1⁻¹ cell water · min⁻¹.

3. 3. The K_m for net exit of d-glucose into solutions containing zero sugar is 15.8 ± 1.7 mM, V 9.3 ± 3.3 mol 9.3 ± 3.3 mol · 1⁻¹ cell water · min⁻¹.

4. 4. This experimental evidence corroborates the previous finding of Hankin, B.L., Lieb, W.R. and Stein, W.D. [(1972) Biochim. Biophys. Acta 255, 126–132] that there are sites with both high and low operational affinities for d-glucose at the inner surface of the human erythrocyte membrane. This result is inconsistent with current asymmetric carrier models of sugar transport.

Structural properties of phospholipids in the rat liver inner mitochondrial membrane. A P-NMR study

1. 1. The ³¹P-NMR characteristics of intact rat liver mitochondria, mitoplasts and isolated inner mitochondrial membranes, as well as mitochondrial phosphatidylethanolamine and phosphatidylcholine, have been examined.

2. 2. Rat liver mitochondrial phosphatidylethanolamine hydrated in excess aqueous buffer undergoes a bilayer-to-hexagonal (H_II) polymorphic phase transition as the temperature is increased through 10°C, and thus prefers the H_II) arrangement at 37°C. Rat liver mitochondrial phosphatidylcholine, on the other hand, adopts the bilayer phase at 37°C.

3. 3. Total inner mitochondrial membrane lipids, dispersed in an excess of aqueous buffer, exhibit ³¹P-NMR spectra consistent with a bilayer arrangement for the majority of the endogeneous phospholipids; the remainder exhibit spectra consistent with structure allowing isotropic motional averaging. Addition of Ca²⁺ results in hexagonal (H_II) phase formation for a portion of the phospholipids, as well as formation of ‘lipidic particles’ as detected by freeze-fracture techniques.

4. 4. Preparations of inner mitochondrial membrane at 4 and 37°C exhibit ³¹P-NMR spectra consistent with a bilayer arrangement of the large majority of the endogenous phospholipids which are detected. Approx. 10% of the signal intensity has characteristics indicating isotropic motional averaging processes. Addition of Ca²⁺ results in an increase in the size of this component, which can become the dominant spectral feature.

5. 5. Intact mitochondria, at 4°C, exhibit ³¹P-NMR spectra arising from both phospholipid and small water-soluble molecules (ADP, P_i, etc.). The phospholipid spectrum is characteristic of a bilayer arrangement. At 37°C the phospholipids again give spectra consistent with a bilayer; however, the labile nature of these systems is reflected by increased isotropic motion at longer (at least 30 min) incubation times.

6. 6. It is suggested that the uncoupling action of high Ca²⁺ concentrations on intact mitochondria may be related to a Ca²⁺-induced disruption of the integrity of the inner mitochondrial phospholipid bilayer. Further, the possibility that non-bilayer lipid structures such as inverted micelles occur in the inner mitochondrial membrane cannot be excluded.

Bioenergetic responses of sub-adult sea cucumber Apostichopus japonicus (Selenka) (Echinodermata: Holothuroidea) to temperature with special discussion regarding its southernmost distribution limit in China

1. This paper investigated the bioenergetic responses of the sea cucumber Apostichopus japonicus (wet weights of 36.5±1.2 g) to different water temperatures (5, 10, 15, 20, 25 and 30 °C) in the laboratory.

2. Results showed that theoretically the optimal temperatures for energy intake and scope for growth (SFG) of sub-adult A. japonicus was at 15.6 and 16.0 °C, respectively. The aestivation threshold temperature for this life-stage sea cucumber could be 29.0 °C by taking feeding cessation as the indication of aestivation.

3. Our data suggests that A. japonicus is thermo-sensitive to higher temperature, which prevents it from colonising sub-tropical coastal zones. Therefore, water temperature plays an important role in its southernmost distribution limit in China.

4. The potential impact of global ocean warming on A. japonicus might be a northward shift in the geographical distribution.

The effect of copper on frog skin. The role of sulphydryl groups

1. 1. Cu²⁺ at a concentration of 10⁻⁴ M, when applied to the external side of the frog skin produces an increase in the short-circuit current (I_sc).

2. 2. This effect was studied in skins of Rana temporaria adapted to cold (5°C) and room temperature (20°C), skins of Rana pipiens adapted to cold, and the results compared with those obtained previously with Rana ribibunda.

3. 3. The observed effect is less dependent upon the adaptation to cold than upon the functional state of the skin: skins with low short circuit currents have a bigger response to Cu²⁺ than skins with high I_sc.

4. 4. A species difference cannot be ruled out since skins of Rana ribibunda exhibiting high I_sc give good responses to Cu²⁺.

5. 5. 5,5′-dithiobis(2-nitrobenzoic acid), a sulphydryl-oxidizing reagent, produces an effect similar to that of Cu²⁺, and dithiothreitol an SH-reducing agent, reverses the effect of this ion.

6. 6. Cu²⁺ also induces an increase in the unidirectional K⁺ fluxes and unmasks a net outward potassium flux.

7. 7. The outward K⁺ flux induced by Cu²⁺ is sensitive to ouabain.

8. 8. It is concluded that Cu²⁺ increases the permeability of the external barrier of the frog skin to Na⁺ and K⁺, probably by reacting with SH groups.

Inverse relationship of protein concentration and binding activity of alpha-galactoside receptors from sugarcane membranes

1. 1. The binding activity of purified α-galactoside receptor proteins from a number of plant species decreases when the protein concentration is increased from 2 ng/ml to 100 μg/ml.

2. 2. The apparent loss of binding activity at high protein concentrations corresponds to the formation of high molecular weight multimers.

3. 3. Raffinose and melibiose cause a ligand-dependent increase in binding activity and a corresponding decrease in the relative abundance of multimers at any given protein concentration.

4. 4. The self-inhibition of binding activity at high protein concentrations arises from a competition between ligand binding by oligomers and self-association of these oligomers into multimeric species which have little or no binding activity.

Association of bacteriorhodopsin with lipid-impregnated filters. Evidence for fusion of bacteriorhodopsin-containing vesicles with the lipid phase of the filter

Bacteriorhodopsin vesicles were associated with cellulose-nitrate filters impregnated with a solution of phospholipids in hexadecane. The generation of (photo)potentials upon illumination of the filter was studied in the absence and presence of ionophores, phospholipase A₂, EDTA or polyene antibiotics.From these experiments the following conclusions are drawn.

1. 1. Upon illumination of the filter, bacteriorhodopsin pumps protons into aqueous compartments located in the filter.

2. 2. These aqueous compartments possibly do not originate from the compartments enclosed by the bacteriorhodopsin vesicles. Evidence is obtained that aqueous compartments are present in the surface layers of the lipid-impregnated filters.

3. 3. The results are explained most easily by a mechanism, whereby fusion occurs between the vesicles and the lipids of the filter.

Determination of calcium transport and phosphoprotein phosphatase activity in microsomes from respiratory and vascular smooth muscle

1. 1. Calcium transport into microsomal vesicles of respiratory (tracheal) smooth muscle was characterized. This calcium transport was ATP dependent and stimulated by the presence of the oxalate ion. The magnitude of transport was similar to that reported for microsomes from other types of smooth muscle.

2. 2. Bovine and rabbit, heavy and light microsomes were isolated from respiratory (tracheal) and vascualar (aortic) smooth muscle. Preincubation of these vesicles with cyclic AMP and protein kinase did not alter the transport of calcium into the vesicles. There was no evidence of phosphate incorporatio into microsomal membrane proteins. Similar results were obtained if phosphorylase b kinase replaced the combination of cyclic AMP and protein kinase during the preincubation.

3. 3. The phosphoprotein phosphatase activity of cardiac sarcoplasmic reticulum and smooth muscle microsomes was determined. The activity of this enzyme was found to be several-fold less in the cardiac sarcoplasmic reticulum than in various smooth muscle microsome preparations.

Chemical modification by trinitrobenzenesulfonate of a lipid and proteins of intracytoplasmic membranes isolated from Chromatium vinosum and Azotobacter vinelandii

1. 1. The structure of intracytoplasmic membranes of a photosynthetic bacterium Chromatium vinosum and a nitrogen-fixing bacterium Azotobacter vinelandii was studied by chemical modification of amino groups of phospatidylethanolamine and proteins with trinitrobenzensulfonate.

2. 2. Almost all the constituents of intracytoplasmic membranes of C. vinosum were solubilized in a mixture of chloroform, methanol and trichloroacetic acid. One-third of proteins in the intracytoplasmic membranes of C. vinosum was found solubilized in a mixture of chloroform and methanol. By using a column chromatography with Sephadex LH-20 in organic solvents, the unmodified as well as the trinitrophenylated proteins and also the trinitrophenylated phosphatidylethanolamine were separated from the other colored substances.

3. 3. In the chemical modification of the intracytoplasmic membrane preparations, 30% of phosphatidylethanolamine and 15% of protein amino groups in C. vinosum and 45% of phosphatidylethanolamine and 20% of protein amino groups in A. vinelandii were estimated to be exposed to the aqueous phase. In the single-layered liposomes composed of phosphatidylethanolamine and phospatidylglycerol with a ratio of 2:1, 40% of phosphatidylethanolamine were estimated to be exposed to the aqueous phase.