THE EFFECTS OF SOLUBILIZATION PROCEDURES ON THE RELEASE AND MOLECULAR STATE OF ACETYLCHOLINESTERASE FROM ELECTRIC ORGAN TISSUE

Abstract— A study was made of the effect of various solubilization procedures on the release of AChE from electric organ tissue of the electric eel and on the molecular state of the enzyme. The procedures employed included homogenization in different ionic media or in the presence of detergents, etuymic treatment and chemical modification. Studies were performed on intact electroplax, tissue homogenates and membrane fractions. The apparent AChE activity of intact cells, homogenates and membrane fractions was shown to be governed by diffusion-controlled substrate and hydrogen ion gradients, generated by AChE-catalyscd hydrolysis, leading to a lower substrate concentration and a lower pH in the vicinity of the particulate enzyme.
Treatment of homogenates with NaCl solutions or with NaCl solutions containing the nonionic detergent Triton X-100 causes release of the native'molecular forms of the enzyme (primarily the 18 S species) which aggregate at low ionic strength. For optimal extraction both high ionic strength (e.g. 1 M-NaCl) and the detergent are needed AChE is also solubilized by treatment of tissue homogenates with trypsin, bacterial protease or collagenase. The first two enzymes caused its release as an 11 S non-aggregating form, while collagenase also produces a minor non-aggregating - 16 S component. Treatment of tissue homogenates with maleic anhydride causes release of AChE as a non-aggregating 18 S species. On the basis of the solubilization experiments it is concluded that the interaction of AChE with the excitable membrane is primarily electrostatic. The possible orientation of the enzyme within the synaptic gap is discussed.     

Electron microscope examination of two plaque variants from a nuclear polyhedrosis virus of the alfalfa looper, Autographa californica

This investigation looks into the ultrastructural differences between plaque variants of the alfalfa looper nuclear polyhedrosis virus. The variants exhibit distinct differences in polyhedra morphology and enveloping of the nucleocapsids.Tissues from larvae infected per os or subcutaneously with virus from one type of plaque always contained virus representative of both plaques. This was not true of the in vitro cultured cells. In those cells, a culture infected with one plaque type always developed infections that were typical of that particular plaque.     

Acrylonitrile inhalation in rats: II. Excretion of thioethers and thiocyanate in urine

In male Wistar rats, the inhalation exposure to acrylonitrile (AN), 271 mg X m-3, 8 hours a day, 5 days a week, did not affect protein sulfhydryl concentration in liver and blood and decreased glutathione concentration in the liver, but not in the brain at the end of the fifth exposure. The urinary excretion of the main AN metabolites, thioethers (AN-mercapturic acids) and thiocyanate was proportional to the inhaled AN concentration (57, 125, 271 mg X m-3, respectively) in a single exposure for 12 hours, and their mutual ratio was greatly different from that after injection of AN. The results revealed that the urinary excretion of thioethers is a very sensitive and dose-related indicator of exposure to AN and extrapolation of the results indicates that the exposure to AN concentration below 10 mg X m-3 could thus be demonstrated.     

Calnexin interaction with N-glycosylation mutants of a polytopic membrane glycoprotein, the human erythrocyte anion exchanger 1 (band 3).

The interaction of the endoplasmic reticulum chaperone calnexin with N-glycosylation mutants of a polytopic membrane glycoprotein, the human erythrocyte anion exchanger (AE1), was characterized by cell-free translation and in transfected HEK293 cells, followed by co-immunoprecipitation using anti-calnexin antibody. AE1 contains 12-14 transmembrane segments and has a single site of N-glycosylation at Asn-642 in the fourth extracytosolic loop. This site was mutated (N642D) to create a nonglycosylated protein. Calnexin showed a preferential interaction with N-glycosylated AE1 relative to nonglycosylated AE1 both in vitro and in vivo. This interaction could be blocked by inhibition of glucosidases I and II with castanospermine. Calnexin had access to novel N-glycosylated sites created in other extracytosolic loops in AE1 by site-directed or insertional mutagenesis. The interaction with AE1 was enhanced when multiple sites were introduced into the same loop or into two different loops. An association of calnexin with truncated versions of N-glycosylated AE1 was detected after release of the nascent chains from ribosomes with puromycin. The results show that the interaction of calnexin with the polytopic membrane glycoprotein AE1 was dependent on the presence but not the location of the oligosaccharide. Furthermore, calnexin was associated with AE1 after release of AE1 from the translocation machinery.