Thermostability of membrane systems in organic solvents

Two multisubunit enzymes of the inner mitochondrial membrane, cytochrome oxidase and the H+-ATPase may be transferred into highly apolar solvents as protein-lipid complexes. At 70 degrees C and an initial water concentration of 13 microliters per ml organic solvent (toluene), the half-life of the ATPase was approx. 11 h, whereas that of cytochrome oxidase was about 100 s. Thermostability of cytochrome oxidase could be increased more than 100-times by decreasing the water concentration to 3 microliters per ml toluene. At this latter concentration of water the half-life of the ATPase at 90, 80 and 70 degrees C was 5, 48 and 96 h, respectively.     

A specific immunological probe for the major myelin proteolipid. Confirmation of a deletion in DM-20

Major myelin proteolipid (MMPL, also called PLP) and DM-20 are the two major intrinsic membrane proteins of CNS myelin. A specific immunological probe was obtained for MMPL by raising antibodies against the synthetic tridecapeptide 117-129 of MMPL. Antibodies against this peptide reacted with the MMPL but did not cross react with DM-20, while both proteolipids had been shown previously to be recognized by antibodies directed against the C-terminal hexapeptide of MMPL. This is in accordance with previous findings showing that DM-20 differs only from MMPL by a deletion of residues 100-140 (+/- few units). Furthermore, this site-specific immunological probe also recognizes MMPL in its native form in oligodendrocytes in primary glial cell cultures.     

ATP-dependent translocation of amino phospholipids across the human erythrocyte membrane

Trace amounts of radiolabeled phospholipids were inserted into the outer membrane leaflet of intact human erythrocytes, using a non-specific lipid transfer protein. Phosphatidylcholine, phosphatidylserine and phosphatidylethanolamine were transferred from the donor lipid vesicles to the membrane of the intact red cell with equal ease, whilst sphingomyelin was transferred 6-times less efficiently. The transbilayer mobility and equilibrium distribution of the labeled phospholipids were assessed by treatment of the intact cells with phospholipases. In fresh erythrocytes, the labeled amino phospholipids appeared to move rapidly towards the inner leaflet. The choline phospholipids, on the other hand, approached an equilibrium distribution which strongly favoured the outer leaflet. In ATP-depleted erythrocytes, the relocation of the amino phospholipids was markedly retarded.     

Atrial natriuretic factor: an overview

Heart atrial muscle cells in mammals are differentiated for a contractile as well as a secretory function. Through the latter, the heart plays an endocrine role; it synthesizes, stores, and releases a group of peptides collectively referred to as atrial natriuretic factor (ANF). ANF has natriuretic and hypotensive properties as well as an inhibitory effect on aldosterone and renin secretion. Thus ANF intervenes in the short- and long-term regulation of water and electrolyte balance and blood pressure. It is expected that further research in this new field will provide fresh insights into the pathophysiology of several important clinical entities and in the development of new pharmaceutical products.     

The similarity principle underlying social bonding among female rhesus monkeys

Twenty adult female rhesus monkeys (Macaca mulatta) were observed over a three-year period. They lived in a mixed captive group with kinship relations known for three generations. The study's aim was to test Seyfarth's [J. theor. Biol. 65: 671-698, 1977] model of rank-related grooming and to investigate two other possible determinants of social bonding, i.e. relative age and the group's stratification into two social classes. Data on affiliation, coalitions, and social competition were collected by means of both focal observation and instantaneous time sampling. Whereas certain elements of the existing model were confirmed, its explanatory principles were not. Social competition did not result in more contact among close-ranking females (the opposite effect was found), and the relation between affiliative behavior and coalitions was more complex than predicted. Based on multivariate analyses and a comparison of theoretical models, we propose a simpler, more encompassing principle underlying interfemale attraction. According to this 'similarity principle', rhesus females establish bonds with females whom they most resemble. The similarity may concern genetical and social background, age, hierarchical position and social class. Effects of these four factors were independently demonstrated. The most successful model assumed that similarity factors influence female bonding in a cumulative fashion.     

Age-sex class differences in the positional behaviour of the Sumatran orang-utan (Pongo pygmaeus abelii) in the Gunung Leuser National Park, Indonesia

During a three-year field study of the socio-ecology of Sumatran orang-utans, their use of the canopy was investigated in the Gunung Leuser National Park, Indonesia. This paper concerns the positional behaviour of different age-sex classes of orang-utans. Adolescents and females with infants differed significantly from an adult male in the following respects: the use of locomotion types (more 'quadrumanous scrambling' and perhaps also 'quadrupedal walking' and less 'tree swaying'); substrate use during resting, and travelling and resting heights. We suggest that large body size restricts the travel route options in higher forest strata and necessitates the use of the lower stratum. Here, 'tree swaying' is an efficient method of progression, particularly for heavy animals. Mothers with infants are forced to travel in the lower zones as well. The fact that they return to a greater heights when they go to rest might suggest that they travel lower in spite of a greater predation risk.     

Comparative study of G- and C-banded chromosomes of five species of Microtidae

G-banded karyotypes were compared in the following species of Microtidae: Microtus nivalis; M. cabrerae; M. arvalis and Arvicola sapidus. Previous observations on A. sapidus and A. terrestris (Díaz de la Guardia & Pretel, Caryologia 32: 183–189, 1979) were also incorporated in this study. The results show that Robertsonian translocations and pericentric inversions are common mechanisms involved in the karyotypic evolution of this group. Interspecific differences in C-banding patterns were also analyzed. Using the karyograph method (Imai et al., Am. Nat. 121: 477–488, 1983), the evolutionary distances of the karyotypes were estimated, and an attempt was made to establish a presumptive phylogenetic tree.     

Reconstitution of the vascular wall in vitro. A novel model to study interactions between endothelial and smooth muscle cells

To study the biology of the endothelium under conditions that mimic the architecture of the vessel wall, endothelial cells were grown on a collagen lattice containing a multilayer of smooth muscle cells. Light and electron microscopy of such cultures revealed a confluent monolayer of flattened endothelial cells. In co-culture, endothelial cells tend to elongate, whereas in the absence of smooth muscle cells, the endothelial cells show the polygonal morphology typical for cultures of endothelial cells grown on polystyrene substrates. As conditioned culture media of endothelial cells contain substances that may both promote or inhibit the growth of smooth muscle cells, the availability of this vessel wall model prompted us to examine to what extent endothelial cells regulate the proliferation of smooth muscle cells when these cells are maintained in co-culture. Here we show that endothelial cells suppress the proliferation of co-existing smooth muscle cells. This finding suggests that under physiological conditions the balance of the action of growth-promoting and growth-inhibiting substances produced by endothelial cells is in favour of the latter.     

Methodological problems in evolutionary biology VII. The species plague

Various philosophers and evolutionary biologists have recently defended the thesis that species are individuals rather than sets. A decade of debates, however, did not suffice to settle the matter. Conceptual analysis shows that many of the key terms involved (individuation, evolutionary species, spatiotemporal restrictedness, individual) are ambiguous. Current disagreements should dissolve once this is recognized. Explication of the concepts involved leads to new programs for philosophical research. It could also help biology by showing how extant controversies concerning evolution may have conceptual rather than factual roots.     

Bilateral brainstem connections of the rat supratrigeminal region

Efferent and afferent connections of the supratrigeminal region were studied in the rat using iontophoretically delivered horseradish peroxidase and Phaseolus vulgaris leuco-agglutinin. Projections of supratrigeminal efferents were found to the contralateral supratrigeminal region, to the ipsi- and contralateral trigeminal motor nuclei and the medullary reticular formation, and to the ipsilateral facial and hypoglossal motor nuclei. Neurons projecting to the supratrigeminal region were located in the contralateral supratrigeminal nucleus, in the ipsilateral mesencephalic trigeminal nucleus and bilaterally in the medullary reticular formation. This organization is discussed with respect to bilateral oral motor control mechanisms.