Is Chordin a morphogen?

Models employing gradients of diffusible morphogens are often invoked to explain regional specification in the early embryo. In these models, a concentration gradient of a secreted factor generates distinct cell fates, based on the differential response of cells to local concentrations of this morphogen. In recent years, there has been a great deal of focus on the factors involved in the dorsoventral patterning of the vertebrate mesoderm and ectoderm. Dorsoventral specification during amphibian gastrulation is regulated by the antagonistic actions of the Bone Morphogenetic Proteins (BMPs) and a number of dorsally expressed inhibitors, including the secreted factor, Chordin. In a recent paper, Blitz and colleagues explore the possibility that Chordin acts as a long-range factor in the amphibian gastrula embryo, to establish a functional gradient of BMP activity.     

Is tubulin a glycoprotein?

[¹⁴C]Glucosamine is incorporated $\text{in vivo}$ in mouse brain into the major protein species present in purified tubulin preparations when analyzed both by sodium dodecyl sulfate polyacrylamide gel electrophoresis and by isoelectric focusing. The radioactivity incorporated into tubulin can be recovered as a mixture of glucosamine and galactosamine.     

Is homocysteine a pro-oxidant?

High plasma homocysteine concentrations have been found to be associated with atherosclerosis and thrombosis of arteries and deep veins. The oxidative damage mediated by hydrogen peroxide production during the metal-catalyzed oxidation of homocysteine is to date considered to be one of the major pathophysiological mechanisms for this association.

In this work, a very sensitive and accurate method was employed to measure the effective production of H₂O₂ during homocysteine oxidation. Furthermore, the interaction of homocysteine with powerful oxidizing species (hypochlorite, peroxynitrite, ferrylmyoglobin) was evaluated in order to ascertain the putative pro-oxidant role of homocysteine.

Our findings indicate that homocysteine does not produce H₂O₂ in a significant amount (1/4000 mole/mole ratio of H₂O₂ to homocysteine). Moreover, homocysteine strongly inhibits the oxidation of luminol and dihydrorhodamine by hypochlorite or peroxynitrite and rapidly reduces back ferrylmyoglobin, the oxidizing species, to metmyoglobin.

All these results should, in our opinion, lead to a rethinking of the commonly held view that homocysteine oxidation is one of the main causative mechanisms of cardiovascular damage.     

What Is a Story?

This paper attempts to discover the criteria by which a listener accepts or rejects an item of oral narrative as being a story. The hypotheses are: (1) such criteria relate to structure rather than content, although the listener does not consciously distinguish structure from content; (2) the structure must have a certain minimal and maximal degree of complexity and be of a certain kind; (3) the criteria will hold cross-culturally. Information gathered from ethnographies and folklore literature is inadequate to confirm the hypotheses, but it does not contradict them. An experiment to test hypotheses (1) and (2) produced a certain degree of negative confirmation: listeners rejected as a story any narrative item which did not conform to the structural criteria regarded as minimal by myself; however, they also rejected items which I regarded as well structured but which were bizarre or nonsensical in content. The confusion of structure and content tended to confirm hypothesis (1).     

Is Moyeria a euglenoid?

Moyeria , with a known age span of Middle Ordovician through Silurian, and normally placed in the acritarchs, may have euglenoid affinities. If this conclusion is correct it represents the oldest freshwater protozoan, because Moyeria is abundant in fluvial beds in Pennsylvania and New York, as well as in nearshore marine beds at many localities elsewhere. Paramecium is the only other typically freshwater protozoan with a pre-Cenozoic fossil record (a single, unillustrated Cretaceous report): euglenoids have rare Cenozoic records. As a freshwater taxon, or one capable of living in freshwaters, Moyeria , regardless of taxonomic assignment, provides further evidence about the early complexity of the freshwater ecosystem. □ Euglenoids, freshwater, Ordovician, Silurian, protozoans, acritarchs.     

Is arginine a protein-denaturant?

Arginine is a useful solvent additive for many applications, including refolding and solubilization of proteins from insoluble pellets, and suppression of protein aggregation and non-specific adsorption during formulation and purification. However, there is a concern that arginine may be a protein-denaturant, which may limit the expansion of its applications. Such concern arises from the facts that arginine decreases melting temperature and perturbs the spectroscopic properties of certain proteins and contains a guanidinium group, which is a critical chemical structure for denaturing activity of guanidine hydrochloride. Here, we show that although arginine does lower the melting temperatures of certain proteins, the extent is insufficient to cause denaturation of proteins at or below room temperature. The proteins described here show enzymatic activity and folded structure in the presence of arginine, although the local structure around aromatic amino acids is perturbed by arginine. Arginine differs from guandinine hydrochloride in the mode of interactions with proteins, which may be a primary reason why arginine is not a protein-denaturant.     

Is Pneumocystis a Plant?

Pneumocystis, an AIDS-associated opportunistic pathogen of the lung has some unusual features. This article focuses on work done by my group to understand the organism's distinct sterols. Although Pneumocystis is closely related to fungi, it lacks the major fungal sterol, ergosterol. Several delta(7) 24-alkysterols synthesized by P. carinii are the same as those reported in some basidiomycete rust fungi. The 24-alkylsterols are synthesized by the action of S-adenosyl-L-methionine:C-24 sterol methyl transferase (SAM:SMT). Fungal SAM:SMT enzymes normally transfer only one methyl group to the C-24 position of the sterol side chain and the cells accumulate C28 24-alkylsterols. In contrast, the P. carinii SAM:SMT and those of some plants catalyze one or two methyl transfer reactions producing both C28 and C29 24-alkylsterols. However, unlike most fungi, plants, and the kinetoplastid flagellates Leishmania and Trypanosoma cruzi, P. carinii does not appear to form double bonds at C-5 of the sterol nucleus and C-22 of the sterol side chain. Furthermore, the P. carinii SAM:SMT substrate preference for C30 lanosterol differs from that of homologous enzymes in any other organisms studied. C31 24-Methylenelanosterol and C32 pneumocysterol, products of SAM:SMT activity on lanosterol, can accumulate in high amounts in some, but not all, human-derived Pneumocystis jiroveci populations.     

Is it a revolution?

Jablonka and Lamb's claim that evolutionary biology is undergoing a ‘revolution’ is queried. But the very concept of revolutionary change has uncertain application to a field organized in the manner of contemporary biology. The explanatory primacy of sequence properties is also discussed.

Is NSF a fusion protein?

N-ethylmaleimide-sensitive fusion protein (NSF) is an ATPase required for vesicular transport throughout the constitutive secretory and endocytic pathways. Recently, NSF has also been implicated in regulated exocytosis in synapses--based on SNAP-mediated binding in vitro to a complex of neurotoxin substrates (termed 'SNAREs'). This work has generated an hypothesis in which the interaction of SNAREs (SNAP receptors) on the vesicle membrane with those on the target membrane forms a docking complex to which SNAPs bind, thus allowing NSF to bind and elicit membrane fusion. However, current evidence supports an earlier, pre-fusion role for NSF. We speculate that this role may be as a molecular chaperone for the membrane docking/fusion machinery.     

Is dynamin really a 'pinchase'?

The motivation for this article was a recent conversation with an author of a major cell-biology textbook who was gratified that the problem of ?pinching off? membrane vesicles from donor membranes had been solved.It was now known, the author claimed, that the large GTPase dynamin was a ?pinchase? severing the necks of budding vesicles.We are concerned that this appealing speculation has been prematurely elevated to cell-biological dogma.Furthermore, by seeing dynamin exclusively as a pinchase we might fail to recognize alternative functions.In this article, we review briefly the evidence that dynamin is a pinchase, discuss some problems with that speculation and show that other possible functions for dynamin may be at least as appealing.     

Is isolabeling a false image?

Isolabeling in Chinese hamster chromosomes was studied by using a new method which enabled clear demarcation of sister chromatids without the usage of tritium label. The method involved continuous labeling of cells with 5-bromodeoxyuridine and staining of fixed chromosomes with acridine orange. Isolabeling was easily observed in chromosome preparations processed according to the conventional autoradiographic methods, especially in cells treated with ethyl methanesulphonate, and its frequency was dependent on the concentration of the drug. On the other hand, no isolabeling was detected in preparations made by the new method, but exchanges of short segments of sister chromatids were observed frequently, depending upon the concentration of ethyl methanesulphonate. These results strongly suggest that isolabeling observable in autoradiographs is a consequence of sister chromatid exchanges combined with image spread that attends autoradiography.