Dihydrofolate reductase: low-resolution mass-spectrometric analysis of an elastase digest as a sequencing tool (Short Communication)

An elastase digest of a protein of unknown structure, dihydrofolate reductase, was studied by mass spectrometry. This soluble digest contained a large number of small peptides in different yields, within the ideal molecular-weight range (200-1200) for mixture-analysis mass spectrometry. Sequences of the major component peptides in the digest are reported.     

ULTRASTRUCTURAL AND BIOCHEMICAL CHANGES IN BROWN FAT IN COLD-EXPOSED RATS

During the first 3 days of exposure of rats to 5°C, the nitrogen concentration of interscapular brown fat increased by 50% and remained at this elevated level for the duration of the 8-wk observation period, while the mass of tissue increased fourfold. The concentration of both DNA and RNA per unit nitrogen reached a maximum after 3 days, then declined; however, the total quantity of each continued to rise. The concentration of various respiratory enzymes decreased during the first few days and then increased, but at different rates. The morphological changes in mature brown fat cells during cold acclimation were observed to be: a reduction in fat droplet size during the first 3 days, followed by a gradual increase in size through 6 wk in the cold; a continual increase in the amount of intermitochondrial ground substance during the first 3 wk, with increased granularity and glycogen content after 1 wk; initial disappearance of glycogen between mitochondria, followed by the reappearance of a few isolated particles in the intermitochondrial ground substance after 1 wk in the cold; initial increase in the density of intramitochondrial matrix for the first 3–4 days, followed by a gradual return to the control density; loss in integrity of mitochondrial outer membranes during the first 4 days, followed by gradual but incomplete restoration; temporary loss of the dense material in lipid droplets during the first 24 hr, with return after 1 wk in the cold; and a 40% increase in mitochondrial diameter within 1 day, followed by a decrease in diameter within 1 wk to a constant value about 15% larger than the controls.     

Some effects of air ions on the activity of rats

A duct system was arranged through which flowed air of controlled ion concentration. In series was a chamber with a flexible dielectric floor which made possible electrical detection of activity.Exposure to various ion concentrations of either polarity produced pronounced effects.In addition to gross motor activity six other behavioural parameters were recorded. The lowest ion concentration were most effective. In addition to presenting a controlled ambient ion concertration the ion current drawn by the animal was measured. This varied markedly from rat to rat.

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Zusammenfassung Ein Kanalsystem zum Durchfluss von Luft bekannter Ionenkonzentration wurde eingerichtet. Angeschlossen war eine Kammer mit einem beweglichen dielektrischen Boden, der die Registrierung der Aktivität von Ratten ermöglichte. Neben der motorischen Aktivität wurden 6 andere Verhaltensformen der Tiere registriert.Die niedrigste Ionenkonzentration war am wirksamsten zur Anregung der Aktivität. Neben der Ionenkonzentration in der Kammer wurde der von den Tieren eingeatmete Ionenstrom gemessen; er variierte stark von Tier zu Tier.

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Resume On a construit un canal dans lequel il est possible de faire circuler de l'air dont la concentration en ions est contrôlable. On y a adjoint une cellule dont le sol est constitué par un diélectrique flexible permettant de déceler électriquement l'activité de petits animaux.En exposant des rats à des concentrations ioniques variables et de polarité différente, on peut constater des effets prononcés sur le comportement des animaux. En effet, en plus de l'activité motrice, on a enregistré six autres formes de ce comportement. Ce sont les plus faibles concentrations qui produisent le plus d'effets. A part la concentration en ions à l'intérieur de la cellule, on a également mesuré la quantité d'ions absorbés par les bêtes par voie respiratoire. Cette quantité varie fortement d'un individu à l'autre.

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This work was supported by Public Health Service Research Grant #AP00305-02 from the Division of Air Pollution, Bureau of State Services and also by a grant from the Atmospheric Science Research Center of the State University of New York.     

Neutral endopeptidase and neurogenic inflammation in rats with respiratory infections

Neuropeptides such as substance P are implicated in inflammation mediated by sensory nerves (neurogenic inflammation), but the roles in disease of these peptides and the peptidases that degrade them are not understood. It is well established that inflammation is a prominent feature of several airway diseases, including viral infections, asthma, bronchitis, and cystic fibrosis. These diseases are characterized by cough, airway edema, and abnormal secretory and bronchoconstrictor responses, all of which can be elicited by substance P. The effects of substance P and other peptides that may be involved in inflammation are decreased by endogenous neutral endopeptidase (NEP; also called enkephalinase, EC 3.4.24.11), which is a peptidase that degrades substance P and other peptides. In the present study, we report that rats with histories of infections caused by common respiratory tract pathogens (parainfluenza virus type 1, rat corona-virus, and Mycoplasma pulmonis) not only have greater susceptibility to neurogenic inflammatory responses than do pathogen-free rats but also have a lower activity of NEP in the trachea. This reduction in NEP activity may cause the increased susceptibility to neurogenic inflammation by allowing higher concentrations of substance P to reach tachykinin receptors in the trachea. Thus decreased NEP activity may exacerbate some of the pathological responses in animals with respiratory tract infections.