A deoxyribonucleic acid-replication intermediate in the growing mosquito.

In previous experiments on growth and aging in the yellow-fever mosquito, Aedes aegypti, a low mol. wt. (500000) DNA species was found in the supernatant fraction after ultracentrifugation of homogenates of rapidly-growing larvae. This DNA species, "sDNA", constituted 30-40% of total DNA in 2-4-day-old larvae, but was less than 5% in older larvae, pupae and adults. We have now isolated and characterized sDNA and initiated experiments to determine its metabolic role. Isolated sDNA has the same physical and chemical characteristics as bulk DNA, "pDNA", and differs only in size. In CsCl isopycnic centrifugation the buoyant densities of sDNA and pDNA were 1.700 and 1.697 g/cm3 respectively. The "melting" temperature of both DNA species was 84 degrees C. Base compositions calculated from these data and other methods were 38.9 mol% of guanine-plus-cytosine for sDNA, and 38.5 for pDNA. Also, the size of newly-synthesized DNA was investigated by pulse-labelling and pulse-chase experiments. In neutral sucrose gradients the labelled DNA component after a 2h pulse had a sedimentation coefficient of about 8S, but after a 4h pulse sedimented in a broad band from 10-19S. In alkaline sucrose gradients a single peak around 7S was observed for pulse times up to 4h. After a 6h pulse and a 1 day "chase", labelled DNA species had sedimentation coefficients ranging from 10-15S in alkaline sucrose, and after a 2-day chase the values were 17-31S, similar to those of pDNA under alkaline conditions. These results suggest that sDNA represents an intermediate form in the replication of DNA in mosquito larvae.     

Clearance of lysosomal hydrolases following intravenous infusion. The role of liver in the clearance of beta-glucuronidase and N-acetyl-beta-D-glucosaminidase.

Certain highly purified forms of rat lysosomal glycosidases, β-glucuronidase and N-acetyl-β-d-glucosaminidase, are rapidly cleared from the circulation following intravenous infusion. Several lines of evidence are presented which indicate that the primary site of enzyme uptake is the liver. Clearance of the two enzymes was unaffected by nephrectomy, whereas it was abolished by evisceration. Tissue distribution experiments with native and [¹²⁵I]β-glucuronidase indicate the liver as the major, if not exclusive, site of enzyme uptake. Experiments with the isolated perfused liver showed clearance of certain enzyme preparations but not others. Those enzymes cleared by the isolated perfused liver were likewise cleared in vivo. Liver fractionation studies following infusion of large doses of β-glucuronidase revealed a rapid, short-lived increase in microsomal β-glucuronidase and a slower but larger increase in lysosomal β-glucuronidase. The results indicate that β-glucuronidase, N-acetyl-β-d-glucosaminidase, and probably other glycosidases are rapidly incorporated into the lysosomal compartment of liver.     

Modifications of drug metabolism by disulfiram and diethyldithiocarbamate. II. D-Glucuronic acid pathway.

Hepatic enzymes connected with the formation and metabolism of free D-glucuronic acid were affected in rats after treatment with disulfiram or diethyldithiocarbamate (300 mg/kg, intragastrically, per day, 4 X). The activities of UDPglucose dehydrogenase, UDPglucuronic acid pyrophosphatase, UDPglucuronosyltransferase and L-gulonate dehydrogenase were enhanced, while those of glucose-6-phosphate dehydrogenase, beta-glucuronidase and D-glucuronolactone dehydrogenase were inhibited. These changes were more pronounced with disulfiram than diethyldithiocarbamate. Treatment with phenobarbital (80 mg/kg, i.p., per day, 4 X) enhanced UDP glucuronosyl-transferase, but brought about different effects on the other enzymes. Concurrent administration of phenobarbital with disulfiram or diethyldithiocarbamate led to potentiation or antagonism of the primary effects of each compound when given alone. The results suggest that activation of the D-glucuronic acid pathway may proceed in various ways, and that it is not necessarily followed by a simultaneous induction of the microsomal mixed-function oxygenase activity.     

The ultrastructure of the small granular, proteinaceous epidermal cells of some British lumbricids (Annelida) and a reassessment of the identity of the so-called albumen cells

The ultrastructure of the small granular, proteinaceous cells of 11 species of lumbricid earthworm is described and no species differences were recorded. The cells are characterized by the presence of membrane-bound, electron dense granules (0.6–0.7 urn in diameter) arising from polarized Golgi systems in close topographical relationship to the granular endoplasmic reticulum. Variations in electron density of the granules appear to be associated with maturation of the granules. The granules show a finely reticular substructure at high magnification. A less than fully mature stage of this cell type is described.
The occurrence of the small granular cell type in the annelids is discussed, as is the possible function of its secretion.
The confusions in the lumbricid literature concerning this cell type are discussed, and the much referred to figure of the 'albumen' cell type in English texts is shown not to be equivalent to the small granular, proteinaceous type referred to in this and a previous histochemical study.     

Membrane-integration Characteristics of Two ABC Transporters, CFTR and P-glycoprotein

To what extent do corresponding transmembrane helices in related integral membrane proteins have different membrane-insertion characteristics? Here, we compare, side-by-side, the membrane insertion characteristics of the 12 transmembrane helices in the adenosine triphosphate-binding cassette (ABC) transporters, P-glycoprotein (P-gp) and the cystic fibrosis transmembrane conductance regulator (CFTR). Our results show that 10 of the 12 CFTR transmembrane segments can insert independently into the ER membrane. In contrast, only three of the P-gp transmembrane segments are independently stable in the membrane, while the majority depend on the presence of neighboring loops and/or transmembrane segments for efficient insertion. Membrane-insertion characteristics can thus vary widely between related proteins.     

Digestive tract motor correlates of vomiting and nausea

The digestive tract from the upper esophageal sphincter to the ileum participates in the vomiting process, but the role of the digestive tract in nausea is unclear. In preparation for vomiting, the proximal stomach relaxes and the small intestine is evacuated orad in a single mass movement by a retrograde giant contraction and caudad in a stripping fashion by a series of phasic contractions. Orad evacuation of the small intestine may not only remove offending substances but may also dilute. or buffer gastric contents with intestinal and pancreaticobiliary secretions. In association with retching and vomiting, the striated muscle of the esophagus contracts longitudinally, pulling the relaxed proximal stomach into the thoracic cavity forming a funnel from stomach to esophagus. However, gastric evacuation does not occur until the hiatal fibers of the diaphragm relax during vomitus expulsion. Nausea is a subjective feeling in humans that is difficult to identify in animals. Various changes in digestive tract activity have been associated with nausea, but no evidence suggests that these events cause nausea. The prodromal signs of vomiting (e.g., increased heart rate and respiration) that occur concomitantly with the gastrointestinal motor correlates of vomiting have been considered autonomic indices of nausea in animals, but this has not been proven. Regardless, the gastrointestinal motor correlates of vomiting do not cause the prodromata. The emetic central pattern generator may be organized in parallel with respect to its individual autonomic correlates, but as groups of responses, the autonomic and somatomotor correlates may be organized in series.