Gangliosides inhibit 125I-labeled thyrotropin binding to the thyrotropin receptors on bovine thyroid plas- ma membranes, on guinea pig retro-orbital tissue plasma membranes, and on human adipocyte membranes. This inhi- bition by gangliosides is critically altered by the number and location of the sialic acid residues within the ganglioside structure, the efficacy of inhibition having the following order: GDlb > GT1 > GM1 > GM2 = GM3 > GDla The inhibi- tion results from the interaction of thyrotropin and ganglios- ides, rather than the interaction of membrane and ganglios- ides. Fluorescence studies show that the inhibition is associ- ated with a distinct conformational change of the thyrotro- pin molecule and that the progression from a noninhibitory conformation to an inhibitory conformation arallels ex- actly the order of effectiveness in inhibiting 125I-Yabeled thy- rotropin binding. The ganglioside inhibition of 125I-labeled thyrotropin binding appears to be hormonally specific in that it is not affected by albumin, glucagon, insulin, prolactin, fol- licle-stimulating hormone, growth hormone, or corticotropin. The possibility that a ganglioside or ganglioside-like struc- ture is a component of the thyrotropin receptor is suggested by the finding that gangliosides more complex than N-acetyl- neuraminylgalactosylglucosylceramide are present in bovine thyroid membranes in much higher quantities than have been previously found in extraneural tissue. The finding that the B component of cholera toxin, which also interacts with gangliosides, has a peptide sequence in common with the : subunit of thyrotropin, suggests that thyrotropin and cholera toxin may be analogous in their mode of action on the mem- brane.
Unlabeled cholera toxin inhibits [125I]thyrotropin binding to thyrotropin receptors on thyroid plasma membranes. Maximal inhibition by cholera toxin does not exceed 40%, whereas unalbeled thyrotropin completely inhibits [125I]thyrotropin binding to these same membranes. Kinetic analyses of the binding data are compatible with the view that the cholera toxin decreases the number of receptor sites available to thyrotropin and that the mechanism by which the cholera toxin inhibits [125I]thyrotropin binding to these receptor sites involves both competitive and noncompetitive elements.
Salmincola californiensis (Dana, 1853) (Subclass Copepoda: Family Lernaeopodidae) is known to parasitize salmonids of the genus Oncorhynchus including Oncorhynchus mykiss (rainbow trout), Oncorhynchus tshawytscha (chinook salmon), and Oncorhynchus kisutch (coho salmon). These 3 salmonids have been introduced to the Great Lakes intermittently since the mid-1800s. As we demonstrate here, the introduction of these salmonids to the Great Lakes was followed, at some point, by the introduction of their parasitic gill copepod, S. californiensis. Given anecdotal accounts of S. californiensis in introduced salmonids in Lake Ontario since 2012, we chose to conduct a survey to formally document the occurrence of this introduced species. Our survey took place during spring, summer, and fall of 2018 and during spring of 2019 at the south-eastern side of Lake Ontario. Prevalence of S. californiensis was 69, with a mean intensity of 2.7 in 61 rainbow trout examined in 2018. In 2019, prevalence of S. californiensis was 71, with a mean intensity of 3.6 in 59 rainbow trout examined. The prevalence of S. californiensis was 39, with a mean intensity of 1.6 in 223 chinook salmon examined in 2018. No specimens of S. californiensis were found in the 100 coho salmon examined in 2018. The prevalence of S. californiensis in rainbow trout is of great concern considering that it is double that found in rainbow trout in the native range (69 [in 2018] and 71 [in 2019] vs. 35). This is the first formal documentation of the invasion of S. californiensis in Lake Ontario. Future fisheries management decisions in Lake Ontario and its tributaries should take into account these data.
Abstract Multiple sclerosis serum contains a factor or factors capable of releasing sequestered [ 14 C]glucose from liposomes containing G M1 , the major ganglioside present in human central nervous system myelin. Although some control sera can also release large quantities of liposomal glucose, multiple sclerosis and control sera differ in the mechanism of this release. Liposomal damage by multiple sclerosis serum does not appear to be complement mediated, but shares certain releasing characteristics of cholera toxin.
Gangliosides inhibit 125I-labeled thyrotropin binding to the thyrotropin receptors on bovine thyroid plasma membranes, on guinea pig retro-orbital tissue plasma membranes, and on human adipocyte membranes. This inhibition by gangliosides is critically altered by the number and location of the sialic acid residues within the ganglioside structure, the efficacy of inhibition having the following order: GD1b greater than GT1 greater than GM1 greater than GM2 = GM3 greater than GD1a. The inhibition results from the interaction of thyrotropin and gangliosides, rather than the interaction of membrane and gangliosides. Fluorescence studies show that the inhibition is associated with a distinct conformational change of the thyrotropin molecule and that the progression from a "noninhibitory conformation" to an "inhibitory conformation" parallels exactly the order of effectiveness in inhibiting 125I-labeled thyrotropin binding. The ganglioside inhibition of 125I-labeled thyrotropin binding appears to be hormonally specific in that it is not affected by albumin, glucagon, insulin, prolactin, follicle-stimulating hormone, growth hormone, or corticotropin. The possibility that a ganglioside or ganglioside-like structure is a component of the thyrotropin receptor is suggested by the finding that gangliosides more complex than N-acetylneuraminylgalactosylglucosylceramide are present in bovine thyroid membranes in much higher quantities than have been previously found in extraneural tissue. The finding that the B component of cholera toxin, which also interacts with gangliosides, has a peptide sequence in common with the beta subunit of thyrotropin, suggests that thyrotropin and cholera toxin may be analogous in their mode of action on the membrane.
