A single spiral artefact in Arthropod cuticle

Spirals are often seen in sections transverse to the axes of bumped structures in arthropod cuticle. (Sections through arthropod cornea or exocones yield excellent examples.) As arthropod cuticle has a helicoidal architecture (Bouligand, 1965), it might be expected that the spirals are a simple consequence of that structure. According to a symmetry argument, the spirals thus predicted must be double spirals. In contrast, the observed spirals are usually single. We propose that the single spirals result from an interaction between the microtome knife and the cuticle architecture. The direction of knife travel defines an orientation within the cuticle, subverting the symmetry arguments that require double spirals. Bouligand (1972) presented a model for the interaction of the knife with the cuticle. However, we offer arguments and observations which show that Bouligand's model is incorrect. We argue from detailed observations of the single spiral that it is indeed a knifing artifact and that its explanation probably lies within a certain class of models. Two related models based on relative movements of cuticle components are examined via computer techniques.     

Ontogenesis of pyruvate kinase in the brain and liver tissues of the rat

The ontogenetic study of pyruvate kinase in the brain and liver tissues was performed in different batches of rats, from the fœtus at the 13th day of gestation to the adult subject.

— According to the kinetic study, the shape of the curve is transformed from sigmoid to hyperbolic from the 13th day of fœtal life to adulthood in the brain. Hill cœfficient increases with the age of animal in the liver tissue.

— According to polyacrylamide gel isoelectrofocusing, a family of four, transitory or definite bands are detected in the fœtal brain: they are well defined by their pHi: M₄, M₃, M₂, M₁; at the adult stage, M₁ predominates, M₂ is minor. Three principal bands are distinguished in the liver: two are characteristic of fœtal life (Lf and M₂), one of adulthood (L).

— According to the immunochemical tests, there are antigenic determinants common to M₁, M₂, M₃ and M₄.

The confrontation of the first two methods prompts the conclusion that the kinetic of the enzyme (and perhaps its function) varies with the animals age and is linked to its molecular structure. With the third method, it allows to stress the precociousness of the appearance of the common antigenic determinants, simultaneously with immature enzymatic forms.The signification of the kinetic modifications as well as the succession of the isozymes of the M type in a determined order are discussed and the in vivo formation of hybrids is suggested.     

Molecular and Supramolecular Architecture of theSalmo gairdneriProteinaceous Eggshell during Development

A detailed developmental study of eggshell architecture of the fishSalmo gairdneri(rainbow trout) was performed using transmission and scanning electron microscopy. Thioglycollic acid treatment and freeze-fracturing reveal that fibrils ca. 5–10 nm in diameter constitute each lamella of the helicoidal eggshell. Freeze-fracturing also permits a direct visualization of the helicoidal architecture. Laser-Raman studies of the eggshell indicate abundant antiparallel β-pleated-sheet conformation in the eggshell proteins ofS. gairdneriduring all developmental stages. Apparently, this conformation dictates formation of the helicoidal structure. Disulfide bonds, together with isopeptide bonds, cross-linkS. gairdnerieggshell proteins throughout development.     

Two separate zones of helicoidally orientated microfibrils are present in the walls ofNitella internodes during growth

Summary The dynamic changes in microfibril architecture in the internode cell walls of the giant unicellular algaNitella translucens were studied during cell expansion. Thin section electron microscopy in conjunction with mild matrix polysaccharide extraction techniques revealed three distinct architectural zones in the walls of fully grown cells. These zones were related to distinct phases of growth by monitoring changes in cell wall architecture of internodes during active cell expansion. The initial microfibril deposition before the onset of active cell growth is helicoidal. A helicoid is a structurally complex but ordered arrangement of microfibrils that has been detected increasingly often in higher plant cell walls. During active cell elongation microfibrils are deposited transversely to the direction of cell elongation as shown in earlier studies by birefringence measurements in the polarizing microscope. The gradual decline in cell elongation corresponds with a final helicoidal deposition which continues after cell expansion ceases entirely.The continual presence of the initial helicoidal zone in the outer wall region during the whole growth process suggests that these microfibrils do not experience strain reorientation and are continually reorganized, or maintained, in a well ordered helicoidal arrangement.     

Fluorimetric determination of the resting potential changes associated with the chemotactic response in Paramecium

1. (1) Evidence is presented which indicates that the carbocyanine dye (3,3′ dipropyl thiadicarbocyanine) can be used as a spectroscopic probe for monitoring the resting potential across the plasma membrane of the ciliated protozoan Paramecium.

2. (2) The dye at low concentrations ( 1 μM) does not affect either the viability or the motility of the cells, nor does it induce a chemotactic response.

3. (3) The fluorescence of the dye bound to the cells alters as the potential across the membrane is changed by increasing the external cation concentration.

4. (4) The absorbance of the bound dye also changes in response to an alteration of the membrane potential.

5. (5) The membrane potential changes as measured by the fluorescence method have been correlated with the measurements of the potential estimated by microelectrode methods.

6. (6) Both cations which induce a negative chemotactic response in Paramecium (K⁺, Na⁺, Ba²⁺) and several non-toxic cations bring about a rapid depolarization of the plasma membrane. The significance of these rapid changes in relation to the swimming behaviour of the ciliate is discussed.

Concentration and shear rate dependence of viscosity in random coil polysaccharide solutions

The concentration (c) and shear rate (γ) dependence of viscosity (η) has been studied for a wide range of random coil polysaccharide solutions, and the following striking generalities are observed:

1. 1. The transition from dilute to concentrated solution behaviour occurs at a critical concentration , when ‘zero shear’ specific viscosity (η_sp) ≈ 10. η_sp varies as c^1.4 for dilute solutions, and as c^3.3 for concentrated solutions.

2. 2. The shear rate dependence of viscosity, and frequency dependence of dynamic (oscillatory) viscosity are closely superimposable.

3. 3. Double logarithmic plots of against (where η₀ is ‘zero shear’ viscosity, and is the shear rate at which ) are essentially identical for all concentrated solutions studied, and thus the two parameters η₀ and completely define the viscosity at all shear rates of practical importance.

Departures from points 1 and 2, but not 3, are observed for concentrated solutions of locust bean gum, guar gum, and hyaluronate at low pH and high ionic strength and are attributed to specific intermolecular associations (‘hyperentanglements’) of longer timescale than non-specific physical entanglements.     

Dual effect of membrane cholesterol on simple and mediated transport processes in human erythrocytes

The influence of cholesterol on simple and facilitated transport processes across the membrane of intact human erythrocytes was studied after graded depletion or enrichment of membrane cholesterol by incubation of the cells in phospholipid or phospholipid/cholesterol suspensions.

1. 1. The carrier-mediated transfer of L-lactate and of L-arabinose proved to be enhanced by cholesterol. In the case of L-lactate, a decrease in K_m seems to be involved in this effect. In contrast, the self-exchange of SO₄²⁻, mediated by the inorganic anion-exchange system, and the simple diffusion of erythritol via the lipid phase of the membrane are inhibited by cholesterol.

2. 2. Reversibility of these two opposite effects of cholesterol was demonstrated by measurements on cells depleted again after cholesterol enrichment and enriched again after previous depletion.

3. 3. Certain phospholipids used for preparing the lipid dispersions that are required for cholesterol variation have effects on permeability of their own, due, for example, to traces of contaminants. A discrimination of such artifacts from the effects of cholesterol is only possible by demonstrating reversibility.

4. 4. The opposite effects of cholesterol on various facilitated transfer processes, which have a correlation in the opposite effects of other modifications of the membrane lipid phase (Deuticke, B., Grunze, M. and Haest, C.W.M. (1979) Alfred Benzon Symposium 14, Munksgaard, Copenhagen, in the press), are indicative of different types of lipid-protein interaction in the erythrocyte membrane.

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.

Helicoidal architecture of fish eggshell

Previous publications show arced patterns in electron micrographs of either microfibrils or canals in sectioned fish eggshells, but these have been misinterpreted. We show here that such patterns in the inner layer of cod (Gadus morrhua), plaice (Pleuronectes platessa) and trout (Salmo gairdneri) eggs arise from a helicoidal structure. This consists of a laminate of protein microfibrils, with the direction of ply processing like the steps of a spiral staircase and with the same sense as a left-handed corkscrew. Mechanically, this is an ideal way to strengthen a spherical shell, to resist deforming forces equally from any direction. Radial canals which traverse this layer are forced into flattened and twisted ribbons. Both the helicoidal microfibrillar structure and the canal shape in fish eggshells show remarkable convergent evolution with similar structures in insect cuticles. Trout eggs were resistant to deforming forces as high as 380,000 N/m². Fish eggshells, like those of many other organisms, are mechanically well designed.     

Helicoidal plane of dental occlusion

A helicoidal plane of postcanine occlusion has been patchily reported in many recent and fossil dentitions of man, and has been suggested as a taxonomic marker distinguishing between the dentitions of Homo and Australopithecines. The present paper describes the helicoidal plane in 19 out of 23 modern human (probably Indian) worn dentitions, in both gracile and robust Australopithecines and in extant anthropoids. It is suggested that tooth wear converts the plane of occlusion present in little-worn teeth, the Monson curve, into a helicoidal plane when 1) the diet is more abrasive, 2) the enamel is thinner and less abrasion resistant, and 3) a longer time separates the eruption of the three molar teeth in a jaw quadrant. A model demonstrates that during the power stroke of a chewing cycle the working side molars move in much the same direction whether the molar occlusal plan follows a Monson curve or a helicoidal plane. The difference is that in the former case the three molars work at the same time while in the latter case they work in sequence from anterior to posterior, thereby concentrating force on one tooth at a time. Because the occlusal plane changes during the life of individuals consuming an abrasive diet, the condition of most anthropoids and hominids, it is argued that the Monson curve has functional significance not because of its influence on occlusal relations and/or jaw movement but because the molar teeth are embedded in bone roughly perpendicular to it, a direction which resists tilting of the teeth during mastication. It is concluded that the helicoidal plane probably has little if any value as a taxonomic marker.     

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.

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.

Changes in the activities of mitochondrial carriers during the development of Xenopus laevis

The transport of the substrates phosphate, pyruvate, malate, fumarate, α-ketoglutarate, citrate, isocitrate and glutamate has been determined in mitochondria isolated from various developmental stages of Xenopus laevis. The carriers may be sub-divided into three groups with respect to the pattern of changes in activity:

1. 1. Pyruvate, tricarboxylate and glutamate/OH carriers, distinguished by low activities during the pregastrula stages and a subsequent increase in activity.

2. 2. Phosphate and α-ketoglutarate carriers, with a constant activity throughout development.

3. 3. Malate and fumarate carriers, highly active initially, but decreasing already after gastrulation.

The results are discussed in relation to mitochondrial differentiation and the change from embryonic to adult metabolism.