Role of cardiotoxin and phospholipase A in the blockade of nerve conduction and depolarization of skeletal muscle induced by cobra venom

1. The effects of phospholipase A (PhA), cardiotoxin (CTX) and neurotoxin (cobrotoxin) isolated from Formosan cobra (Naja naja atra) venom on conduction of the rat phrenic nerve and membrane potential of the rat diaphragm were studied.2. Phospholipase A, lysolecithin and cobrotoxin were without effect on the axonal conduction. Cardiotoxin was the only active agent in cobra venom, but it was less potent than the crude venom.3. The blocking action of cardiotoxin was markedly accelerated by the simultaneous administration of phospholipase A. However, the minimum effective concentration of cardiotoxin (100 mug/ml), was not decreased by phospholipase A. Pretreatment of the nerve with phospholipase A, followed by washout, did not alter the activity of cardiotoxin.4. Cardiotoxin (3 mug/ml) completely depolarized the membrane of superficial muscle fibres within 60 min, being 3 times more potent than the crude venom. Phospholipase A, on the other hand, needed a dose 30 times higher and a prolonged period of incubation to induce depolarization of similar extent. Cobrotoxin was without effect on membrane potentials.5. CaCl(2) (10 mM) effectively antagonized the nerve blocking as well as the depolarizing effect of the crude venom, cardiotoxin or cardiotoxin plus phospholipase A. By contrast, the slow depolarizing effect of phospholipase A was enhanced by high concentrations of calcium.6. Cardiotoxic fractions of Indian cobra venom affected both nerve conduction and diaphragm membrane potential in exactly the same way as cardiotoxin. Toxin A of the same venom was without effect.7. It is concluded that the active agent in cobra venoms either on axonal conduction or on muscle membrane is cardiotoxin. The synergistic effect of phospholipase A on cardiotoxin appears to be due to acceleration rather than potentiation of its action. The mechanism of action of cardiotoxin and its synergism by phospholipase A are discussed.

Promotion of crown-gall tumor growth by lysopine, octopine, nopaline, and carnosine

The growth of crown-gall tumors on primary bean leaves (Phaseolus vulgaris L. cv. "Pinto") was promoted by the addition of d-lysopine, d-octopine, l-carnosine, or nopaline. Assayed on tumors induced by Agrobacterium tumefaciens strain B6, the relative activity was octopine = carnosine > lysopine >> nopaline; assayed on tumors induced by A. tumefaciens strain T-37, which induces tumors which form nopaline, the relative activity was nopaline = octopine = carnosine > lysopine. From one to three applications of carnosine or octopine gave equal additive increments in tumor growth, showing that a continual supply of these substances is required to maintain an increased rate of growth. At concentrations above 0.1 mm, pairs of these growth-promoting substances were less active than when applied singly. Inhibition of octopine-induced growth was obtained by applying 0.01 mm carnosine with 1 mm octopine and partial inhibition was obtained when carnosine was added 10 hr after octopine. Equimolar mixtures of lysopine, octopine, and carnosine, however, were at least as active in promoting tumor growth as any of the compounds added singly at equivalent concentrations. The activity of 0.1 to 0.5 mm lysopine, octopine, and carnosine was inhibited, respectively, by 1 mml-lysine, l-arginine, and l-histidine and this inhibition was limited in each case to the basic amino acid corresponding to that of the growth factor. Arginine fully inhibited octopine-induced tumor growth when applied as much as 6 hr after octopine, indicating that this inhibition was not due to prevention of octopine uptake. Although four separate substances were found which promoted tumor growth, the molecular specificity required for activity of each compound was high. Evidence is presented which suggests that a tumor growth-promoting substance extracted from tumorous leaves is a carnosine-like derivative of l-histidine.

Studies on the status of free amino and carboxyl groups in cobrotoxin

The status of free amino groups in cobrotoxin was studied by stepwise modification with trinitrobenzene sulfonate. Lys-27 was selectively modified without altering the activity of cobrotoxin. However, complete loss of activity was observed when Lys-27 and Lys-47 were trinitrophenylated, suggesting that the epsilon-amino group of Lys-47 is essential for the activity of cobrotoxin. The alpha-amino group of N-terminal leucine had no correlation with activity, demonstrated by the guanidination of the lysine residues with O-methylisourea followed by trinitrophenylation of the alpha-amino group. The carboxyl groups in cobrotoxin were modified with glycine methyl ester after activation with water-soluble carbodiimide. Six out of seven free carboxyls reacted in the absence of guanidine.HCl without altering the biological activity. When the remaining carboxyl was modified in the presence of 5 M guanidine.HCl, the resulting toxin was devoid of activity. This "buried" carboxyl is essential for activity and was identified as the gamma-carboxyl group of Glu-21.

Antagonism by propranolol of the inhibitory effect of phenoxybenzamine on noradrenaline uptake in vivo

The reduction of noradrenaline stores and [3H]noradrenaline concentration in the heart of mice and rats induced by phenoxybenzamine-treatment, alone or in combination with cold-stress, was prevented by propranolol. Propranolol also antagonized a similar effect induced by phentolamine but not that induced by other noradrenaline uptake inhibitors, such as desipramine, cocaine, guanethidine and reserpine. Analysis of the time-course of antagonism by propranolol indicates that it was evident only when the β-adrenoceptor blocking agent remained in the body. The inhibitory effect of phenoxybenzamine on noradrenaline stores reappeared when propranolol was excreted. Propranolol alone did not change cardiac noradrenaline stores or [3H]noradrenaline. It is concluded that the restoration of reflexly increased adrenergic discharge to normal, because of unmasking of spare α-adrenoceptors resulting from β-adrenoceptor blockade by propranolol rather than competition for binding at the active site of phenoxybenzamine, is responsible for the observed antagonism.

The isolation and specificity of alfalfa lipoxygenase

Partial purification of the lipoxygenase from alfalfa seed was accomplished by fractionation of the protein with (NH4)2SO4, phosphate, heavy metal salts and ultracentrifugation. About 24% of the original activity was recovered. The partially‐purified alfalfa lipoxygenase enzyme was free of hydroperoxide‐decomposing activity and was used to determine the positional specificity of linoleic acid oxidation by alfalfa lipoxygenase. Combined gas liquid chromatography‐mass spectrometry was used to analyze known mixtures of 10‐ and 12‐hydroxystearic acid derivatives and was satisfactory for the quantitative determination of the ratio of each component. This combination was used to analyze mixtures containing position isomers of hydroxy fatty acids without separation of each individual compound by other methods. Hydroperoxides produced from linoleic acid oxidation catalyzed by alfalfa lipoxygenase were converted by sodium borohydride reduction, catalytic hydrogenation and bis(trimethylsilyl)acetamide silylation to their corresponding trimethylsilyl either esters and the positional distribution was studied. The 9‐ and 13‐linoleate hydroperoxides produced by alfalfa lipoxygenase were in equal concentrations (50∶50) whereas the distribution for soybean lipoxygenase was 70% 13‐ and 30% 9‐hydroperoxides.

Effects of antigonadotrophins on ovarian function

Immunologic techniques have proven to be useful tools in characterizing the action of pituitary protein hormones on the target organs. Specifically, an antibody to luteinizing hormone can prevent ovulation, delay implantation, or cause fetal resorption depending on the time of administration of the antiserum to female rats. The immunologic interference with ovarian function appears to be associated with the steroidogenesis process during early pregnancy, and with fetal placental function during mid pregnancy in the rat. Progesterone synthesis is diminished, probably by the prevention of luteinizing hormone from stimulating the <i>&#916;</i>⁵&#914; hydroxysteroid dehadrogenase within the interstitial tissue of the ovary. In later pregnancy, the antibody combines with specific cells within the placenta, thereby eliminating any placental influence on the ovarian steroidogenic process.

Modulation of noradrenaline incorporation by nerve activities in the rat submaxillary gland

1. Rats were anaesthetized with chloralose and prepared for electrical stimulation of the cervical sympathetic trunk. The effect of such stimulation was studied on the incorporation of intravenously infused [(3)H]noradrenaline, [(3)H]adrenaline or [(3)H]dopamine by the submaxillary gland.2. A train of 200 stimuli every min for 30 min at 20/sec increased the total incorporation of [(3)H]noradrenaline by 92% over the unstimulated side of the gland, at 50/sec by about 200% and at 3.3/sec by about 30%. The incorporation of [(3)H]adrenaline and of [(3)H]dopamine was also increased by sympathetic stimulation.3. The increases in unaltered [(3)H]noradrenaline and its metabolites were proportional to the increase in total radioactivity.4. Mean venous outflow from the gland was decreased by 15-30% by the sympathetic stimulation.5. After elimination of extraneuronal binding of noradrenaline by ligation of the common excretory ducts, nerve stimulation still increased incorporation.6. Inhibition of normetanephrine production by pyrogallol did not antagonize the nerve impulse-mediated increase of [(3)H]noradrenaline incorporation. alpha-Methyltyrosine was also without effect.7. Desmethylimipramine and bretylium completely abolished the nerve impulse-mediated increase of [(3)H]noradrenaline incorporation in concentrations which did not affect the control uptake or abolish adrenergic transmission.8. Reserpine, guanethidine and phenoxybenzamine antagonized both the control and nerve impulse-mediated incorporations of [(3)H]noradrenaline.9. The results indicate that nerve impulses modulate the incorporation of transmitter amine at the neuronal membrane. Possible mechanisms for this modulation are discussed.

Biogenesis of oxalate in plant tissues

Red beet root discs aerated in potassium phosphate for 2 to 3 days and young spinach leaves actively produce oxalate. A series of labeled compounds was supplied to each of these tissues to determine the extent of conversion to oxalate. Similar results were obtained with the 2 tissues except that in the leaf tissue glyoxylate and glycolate were outstandingly good precursors. Carbon from glucose, acetate, and particularly from some acids of the tricarboxylic acid cycle was recovered in oxalate. Extracts from both tissues were found to contain an enzyme which converts oxaloacetate to oxalate and acetate. The enzyme was partially purified and some of its properties are described. A pathway of oxalate synthesis which does not include glycolate or its oxidase is therefore proposed.