Unidirectional rotary motion in a molecular system.

The conversion of energy into controlled motion plays an important role in both man-made devices and biological systems. The principles of operation of conventional motors are well established, but the molecular processes used by 'biological motors' such as muscle fibres, flagella and cilia to convert chemical energy into co-ordinated movement remain poorly understood. Although 'brownian ratchets' are known to permit thermally activated motion in one direction only, the concept of channelling random thermal energy into controlled motion has not yet been extended to the molecular level. Here we describe a molecule that uses chemical energy to activate and bias a thermally induced isomerization reaction, and thereby achieve unidirectional intramolecular rotary motion. The motion consists of a 120 degrees rotation around a single bond connecting a three-bladed subunit to the bulky remainder of the molecule, and unidirectional motion is achieved by reversibly introducing a tether between the two units to energetically favour one of the two possible rotation directions. Although our system does not achieve continuous and fast rotation, the design principles that we have used may prove relevant for a better understanding of biological and synthetic molecular motors producing unidirectional rotary motion.     

Possible involvement of indolamines in the glycogenic effect of the convulsant methionine sulfoximine in rat brain.

The aim of the present investigation was to look for the mechanisms causing disturbances in carbohydrate metabolism during the action of the epileptogenic agent methionine sulfoximine. The levels of glucose, glycogen, and indolamines were measured in seven different regions of rat brain. Methionine sulfoximine induced a decrease in serotonin level which was roughly dose-dependent. There were no obvious changes in tryptophan and 5-hydroxyindoleacetic levels in any area. Methionine sulfoximine induced the known increase in glucose and glycogen levels. The direct precursor of serotonin. 5-hydroxytryptophan, and benserazide (a decarboxylase inhibitor) were then injected into rats in association with methionine sulfoximine. In this case, methionine sulfoximine failed to induce seizures. Moreover, the serotonin level was unchanged and the carbohydrate content did not significantly increase. There was only a rise in 5-hydroxyindoleacetic acid level. This work shows a striking parallelism between serotonin decrease and glycogen increase.     

Transparency and coherence in human motion perception

When confronted with moving images, the visual system often must decide whether the motion signals arise from a single object or from multiple objects. A special case of this problem arises when two independently moving gratings are superimposed. The gratings tend to cohere and move unambiguously in a single direction (pattern motion) instead of moving independently (component motion). Here we report that the tendency to see pattern motion depends very strongly on the luminance of the intersections (that is, to regions where the gratings overlap) relative to that of the gratings in a way that closely parallels the physics of transparency. When the luminance of these regions is chosen appropriately, pattern motion is destroyed and replaced by the appearance of two transparent gratings moving independently. The observations imply that motion detecting mechanisms in the visual system must have access to tacit 'knowledge' of the physics of transparency and that this knowledge can be used to segment the scene into different objects. The same knowledge could, in principle, be used to avoid confusing shadows with real object boundaries.     

D-Amino acids in mouse tissues are not of microbial origin

Summary Neutral free D-amino acid contents in the serum, kidney, liver, brain, small intestine and urine in germ-free mice and those in specific pathogen-free mice were compared. No significant difference was found. This strongly suggests that the free D-amino acids which were shown to be present in mice in our previous work^{1, 2} did not originate from the enteric microbial flora.     

Moderate cooling depresses the accumulation and the release of newly synthesized catecholamines in isolated canine saphenous veins

Moderate cooling (from 37 degrees to 24 degrees C) depressed the formation of 3H-dopamine and 3H-norepinephrine from 3H-tyrosine by isolated canine saphenous veins. Cooling reduced the evoked release of newly synthesized catecholamine to the same extent as that of stored norepinephrine. Hence the augmentation by cold of the contractile response to sympathetic nerve stimulation observed in earlier work is not accompanied by an augmented release of newly synthesized norepinephrine.     

Cigarette smoke induces DNA single-strand breaks in human cells

Epidemiological evidence suggests that smoking is a major cause of human lung cancer. However, the mechanism by which cigarette smoke induces the cancer remains obscure, although in tobacco carcinogenesis, promotion and/or co-carcinogenesis may have crucial roles. The epidemiological data show that if an individual stops smoking, the risk of his contracting lung cancer increases no further. Moreover, laboratory experiments show that cigarette smoke condensate (CSC) exhibits co-carcinogenic and promoting activities in tumour production and malignant transformation. Clastogenic action is thought to be intimately involved in tumour promotion, and it is therefore interesting that visible chromosome changes such as chromosome aberrations and sister chromatid exchanges are known to be caused by cigarette smoke. However, there has been no previous direct demonstration that cigarette smoke can cause single-strand breaks (SSB) in DNA. Here we report that cigarette smoke induces considerable numbers of DNA SSB in cultured human cells, and that such strand breaks may be ascribed to active oxygen generated from cigarette smoke.     

I-J epitopes are adaptively acquired by T cells differentiated in the chimaeric condition

I-J has been defined as a locus mapped in the murine major histocompatibility complex (MHC) which encodes serological markers found primarily on the surface of suppressor T cells (TS) and soluble suppressor factors (TSF). Recent studies have, however, revealed that there is no such specialized locus within the MHC at the DNA level. As the existence of I-J determinants at the protein level on functional T cells, T-cell clones and hybridomas has been confirmed by several serological and biochemical studies, this contradiction has raised serious arguments in the immunological community concerning the nature, origin and expression of I-J determinants. We have raised a number of monoclonal antibodies against the polymorphic structure of I-J molecules, and have studied the expression of I-J epitopes on T cells derived from irradiated bone marrow chimaeras in which stem cells of different genotype differentiated into T cells under the foreign host MHC environment. The results, presented here, indicate that I-J epitopes are not primarily determined by the MHC genes of the stem cells themselves, but are adaptively acquired by T cells differentiated in the chimaeric condition according to the environmental MHC phenotype. Thus, the serologically detectable I-J epitopes are found to be associated with inducible T-cell receptors recognizing self class II MHC antigens.     

The effect of sulfhydryl compounds on the catalytic activity of Cu, Zn-superoxide dismutase purified from rat liver

Sulfhydryl compounds such as reduced glutathione, cysteine and 2-mercaptopropionylglycine, a hepato-protective agent, activated Cu, Zn-superoxide dismutase purified from rat liver at low concentrations (below 10 microM). Furthermore we found evidence indicating that this activation is achieved by reducing Cu2+ present in the catalytic site of the dismutase, and thereby promoting the dismutation of superoxide anions.