Actin filaments in the acrosomal reaction of Limulus sperm. Motion generated by alterations in the packing of the filaments. (1/78)

When Limulus sperm are induced to undergo the acrosomal reaction, a process, 50 mum in length, is generated in a few seconds. This process rotates as it elongates; thus the acrosomal process literally screws through the jelly of the egg. Within the process is a bundle of filaments which before induction are coiled up inside the sperm. The filament bundle exists in three stable states in the sperm. One of the states can be isolated in pure form. It is composed of only three proteins whose molecular weights (mol wt) are 43,000, 55,000, and 95,000. The 43,000 mol wt protein is actin, based on its molecular weight, net charge, morphology, G-F transformation, and heavy meromyosin (HMM) binding. The 55,000 mol wt protein is in equimolar ratio to actin and is not tubulin, binds tenaciously to actin, and inhibits HMM binding. Evidence is presented that both the 55,000 mol wt protein and the 95,000 mol wt protein (possibly alpha-actinin) are also present in Limulus muscle. Presumably these proteins function in the sperm in holding the actin filaments together. Before the acrosomal reaction, the actin filaments are twisted over one another in a supercoil; when the reaction is completed, the filaments lie parallel to each other and form an actin paracrystal. This change in their packing appears to give rise to the motion of the acrosomal process and is under the control of the 55,000 mol wt protein and the 95,000 mol wt protein.  (+info)

The structure of arthropod and mollusc hemocyanins. (2/78)

The hemocyanins from molluscs and from arthropods differ in the size of their polypeptide chains. A variety of physical techniques including sodium dodecyl sulfate polyacrylamide gel electrophoresis and column chromatography in sodium dodecyl sulfate and guanidine HCl indicate that the polypeptide chain of mollusc hemocyanin has a molecular weight of 290,000. These results were corroborated by quantitative end group analyses. Several experiments designed to count the number of tryptophan and methionine-containing peptides in the hemocyanin from the whelk Busycon canaliculatum indicate that sequence homology within the polypeptide chain of the mollusc hemocyanins accounts for their large size. Digestion of the native protein with subtilisin produces a 50,000-dalton fragment in high yield which corresponds to one binding site for oxygen. On the other hand, the polypeptide chain molecular weight of lobster hemocyanin is 76,000 to 78,000 and this seems to be a general property of all arthropod hemocyanins. The pigment from lobster consists of two very similar polypeptide chains which are not present in equal amount. Analysis of the cysteine-containing and of the tryptophan-containing tryptic peptides confirms the value of the molecular weight. However, separation of fragments which contain methionine indicates that there is sequence homology withing the polypeptide chain of this protein. It is concluded that the mollusc and arthropod hemocyanins have little structural similarity.  (+info)

Sialyl residues in hepatitis B antigen: their role in determining the life span of the antigen in serum and in eliciting an immunological response. (3/78)

Hepatitis B surface antigen was adsorbed to insolubilized sialic acid-specific haemagglutinin isolated from the haemolymph of Limulus polyphemus. Treatment of the antigen with Vibrio cholerae neuraminidase (EC resulted in the release of sialic acid and in an increase of the isoelectric point from pH 4-35 (for subtype ad) or 4-9 (for subtype ay) to pH 5-45. Treated, but not untreated, antigen incorporated [14-C]-sialic acid when incubated at 37 degrees C with sialyl transferase (EC and cytidine-5'-monophosphate-[14-C]-sialic acid. The major portion of [14-C]-sialic acid was linked to a glycoprotein with an apparent mol. wt. of 26 x 10-a. De-sialylated antigen had a drastically reduced in vivo life span in rabbit plasma and elicited a higher humoral antibody response than intact antigen (subtype ad). Antigen-stimulated proliferation of lymphocytes, measured 3 months after immunization, was observed only with cells from rabbits injected with neuraminidase-treated antigen.  (+info)

A novel quinoline alkaloid possessing a 7-benzyl group from the centipede, Scolopendra subspinipes. (4/78)

The novel quinoline alkaloid scolopendrine was isolated from the centipede, Scolopendra subspinipes mutilans L. Koch. The structure was determined to be 2-hydroxy-7-[(4-hydroxy-3-methoxyphenyl)methyl]-3-methoxy-8-quinolyl sulfate on the basis of high-resolution electron-spray ionization mass spectroscopy and two-dimensional NMR spectral data. Unlike quinoline alkaloids so far reported, scolopendrine is unique in having a 7-benzyl moiety in the quinoline ring.  (+info)

Properties of visual cells in the lateral eye of Limulus in situ. (5/78)

Excitatory properties of visual cells in the lateral eye of Limulus, investigated by optic nerve recordings in situ, differ significantly from the properties of cells in the classical, excised eye preparation. The differences suggest the possibility that two receptor mechanisms function in the eye in situ: one mechanism encodes low light intensities and the other responds to high intensities. The two mechanisms enable each ommatidium to respond over an intensity range of approximately 10 log units. This hypothesis was tested by measuring the increment threshold and the spectral sensitivity, by studying light and dark adaptation, and by analyzing the variability of the impulse discharge. Although the results do not conclusively identify two receptor mechanisms, they indicate that a process or a part of a process that functions in the eye in situ is abolished by excising the eye or cutting off its blood supply.  (+info)

Specific effect of neuraminidase on blastogenic response of sensitized lymphocytes. (6/78)

The blastogenic response of sensitized lymphocytes from guinea-pigs to 'de novo' antigens (KLH, HCH and PPD) was ehhanced by BCN treatment in twenty-one of twenty-three instances. In contrast, no effect of VCN on nonsensitized guinea-pig lymphocyte response to these antigens, or to mumps antigen, was noted in any of thirty-four instances, These findings indicate that the enhancement effect of VCN is specific for sensitized lymphocytes. Heating VCN at 100 degrees for 10 minutes completely abolished the enhancement effect on the lymphocyte response. VCN treatment did not change the kinetics of antigen-induced blastogenesis. The increased lymphocyte response could probably be related to unmasking of the antigen receptor sites of the cells, resulting in increased antigen uptake, following the VCN treatment.  (+info)

Endotoxin as a cause of aseptic meningitis after radionuclide cisternography. (7/78)

The role of pyrogens in aseptic meningitis after radionuclide cisternography was studied by means of the Limulus test, a sensitive detector of endotoxin. During a 15-month period, 39 reactions associated with cisternography were reported. Ten samples of specific lots of the radioactive drugs implicated in 20 of these reactions were tested and all reacted strongly positive to the Limulus test. The less sensitive rabbit pyrogen test was negative for these preparations when tested on a dose-per-weight basis. Our findings apparently provide clinical evidence for the observation made in animals that endotoxin is at least 1,000 times more toxic intrathecally than intravenously. The data implicate endotoxin contamination as a cause of adverse reactions to radionuclide cisternography. We conclude that the USP pyrogen test is insufficiently sensitive for intrathecal injectables and should be supplemented by the Limulus test.  (+info)

Light-induced changes of sensitivity in Limulus ventral photoreceptors. (8/78)

The responses of Limulus ventral photoreceptors to brief test flashes and to longer adapting lights were measured under voltage clamp conditions. When the cell was dark adapted, there was a range of energy of the test flashes over which the peak amplitude of the responses (light-induced currents) was directly proportional to the flash energy. This was also true when test flashes were superposed on adapting stimuli but the proportionality constant (termed peak currently/photon) was reduced. The peak current/photon was attenuated more by brighter adapting stimuli than by less bright adapting stimuli. The peak current/photon is a measure of the sensitivity of the conductance-increase mechanism underlying the light response of the photo-receptor. The response elicited by an adapting stimulus had a large initial transient which declined to a smaller plateau. The peak current/photon decreased sharply during the declining phase of the transient and was relatively stable during the plateau. This indicates that the onset of light adaptation is delayed with respect to the onset of the response to the adapting stimulus. If the adaptational state just before the onset of each of a series of adapting stimuli was constant, the amplitude of the transient was a nearly linear function of intensity. When the total intensity was rapidly doubled (or halved) during a plateau response, the total current approximately doubled (or halved). We argue that the transition from transient to plateau, light-elicited changes of threshold, and the nonlinear function relating the plateau response to stimulus intensity all reflect changes of the responsiveness of the conductance-increase mechanism.  (+info)