Dissociation of oxytocin and vasopressin from their carrier protein by chromatography on sephadex G-25

The composition of crystalline complexes of neurophysin-M with [8-arginine]-vasopressin and oxytocin

Neurophysin-M, a methionine-containing protein that is the major constituent of neurophysin, has been crystallized as complexes with [8-arginine]-vasopressin. Three moles of vasopressin alone or 2 moles of vasopressin together with 1 mole of oxytocin are bound/mole of protein. An amorphous complex of the protein with oxytocin alone contains 2 moles of the hormone/mole of protein. Deamino-[8-arginine]-vasopressin, a highly active basic analogue of vasopressin, is not bound by neurophysin. The primary amino group of both vasopressin and oxytocin is necessary for binding with neurophysin.

Methods for investigating peptide precursors in the hypothalamus

In conclusion, as in the aminergic nervous system, the hypothalamic neuropeptides "turn over" at a rate sufficient to maintain a "steady state" concentration within the hypothalamus. However, unlike catecholamine-secreting neurons, the brain peptides are synthesized and secreted by a much more circuitous mechanism, involving ribosomal biosynthesis as larger prohormones, axonal transport to the site of secretion, and enzymic processing to the biologically active hormones. The methods described here, including in vitro incubation and high-performance size-exclusion and reverse-phase chromatography, have been found to be useful for examining and comparing the rate and mechanism of biosynthesis of several hypothalamic neuropeptides.

Direct detection of the vasopressin precursor

Cysteine-rich proteins were isolated from the hypothalamo-neurohypophyseal tract of dogs by high performance molecular weight chromatography. Trypsin digestion of these proteins produced a low molecular weight (LMW) peptide which was identified, by chemical and immunological assays, as (Arg8) vasopressin. There appear to be two forms of the precursor protein, one which has vasopressin immunoreactivity, and one which does not. Trypsin digestion of this latter protein produces high as well as LMW immunoreactivity. This suggests that the non-immunoreactive protein may be the precursor to the immunoreactive protein.

Co-operative binding of oxytocin to bovine neurophysin II

The interaction of oxytocin with bovine neurophysin II in 0.1 M-sodium phosphate, pH 5.8, was investigated by equilibrium-dialysis and sedimentation studies. Sigmoidality of the binding curve is attributed to isomerization, either hormone-induced or pre-existing, with preferential binding of oxytocin to one isomeric state. Results are consistent with a binding equation of the form r = (2P[S]+2PQ[S]2)/(1+2P[S]+PQ[S]2) and values of 0.7 X 10(5)M-1 and 1.3 X 10(5)M-1 for P and Q respectively. The significance of these two parameters in relation to current theories of allostery is also discussed.

Neurophysins and posterior pituitary hormones in the suiformes

The neurophysins are proteins that bind the posterior pituitary hormones within the neurosecretory vesicles of the vertebrate neurohypophysis. In the pig, immunofluorescence localization of porcine neurophysin II suggests that this protein is stored with [8-lysine]-vasopressin (LVP). Gel electrophoresis and immunodiffusion of neurohypophysial proteins from two other Suiformes species, the hippopotamus and warthog, hitherto thought to contain LVP, reveal that the warthog has a protein electrophoretically and immunologically identical with porcine neurophysin II, whereas the neurohypophysial proteins of the hippopotamus do not cross-react with a rabbit antiserum specific to this protein. The vasopressins of the hippopotamus and warthog have been recharacterized by gel filtration and by thinlayer chromatography in two solvent systems not hitherto used for this purpose. The presence of LVP in the warthog has been confirmed, but only [8-arginine]-vasopressin (AVP) was detected in the hippopotamus. This suggests that the hippopotamus possesses only AVP, or that the occurrence of LVP in this species is sufficiently rare to make it undetectable by the above techniques. The two species of the Family Suidae studied, i. e. the pig and the warthog, thus seem to be closely related to the structure of their vasopressins and neurophysins, whereas the hippopotamus (Family Hippopotamidae) is less closely related, and seems in this respect to be more similar to other Artiodactyls. This contrasts with the earlier identification of the hippopotamus vasopressin as LVP, which gave biochemical support for the inclusion of the Hippopotamidae within the Suiformes. The weight of the biochemical evidence now favours a contrary view.

Tentative identification of a vasopressin-neurophysin and an oxytocin-neurophysin in the rat

1. Rat neurohypophysial extracts have been examined by polyacrylamide-gel electrophoresis. 2. Three of the proteins were tentatively identified as neurophysins by their acidic nature and their disappearance after dehydration of the animals. 3. These proteins were radioactive 24h after intracisternal injection of [(35)S]cysteine. 4. Two of the proteins were present in much greater quantities than the third, and these two were present in the gland in the same ratio as the hormones vasopressin and oxytocin. 5. One of these proteins was absent from glands of rats homozygous for diabetes insipidus but present in heterozygous animals. 6. It is suggested that these two proteins are the vasopressin-neurophysin and oxytocin-neurophysin of the rat.

The isolation of three neurophysins from porcine posterior pituitary lobes

1. Three neurophysins, proteins that bind the polypeptide hormones oxytocin and vasopressin, have been isolated from acetone-dried porcine posterior pituitary lobes. The proteins have been named porcine neurophysins-I, -II and -III in order of their electrophoretic mobilities at pH8.1. 2. Electrophoretic comparison of the purified proteins, which are homogeneous on starch-gel electrophoresis, with the soluble proteins of fresh porcine posterior pituitary lobes extracted in 0.1m-HCl and in buffer pH8.1 suggests that the isolated proteins are native to the fresh tissue. 3. Neurophysins-I and -II are present in similar amounts in the tissue, whereas neurophysin-III is present only in small quantities. Acetone-dried tissue also contains traces of other hormone-binding neurophysin components. 4. All the neurophysins can bind both oxytocin and [8-lysine]-vasopressin. 5. The apparent molecular weights of the neurophysins increase with increasing protein concentration as measured by equilibrium sedimentation in the ultracentrifuge. 6. Neurophysins-I and -III are of similar molecular dimensions, contain one residue of methionine per molecule and lack histidine. The minimum molecular weight of neurophysin-I obtained by amino acid analysis is 9360. Neurophysin-II is of larger molecular dimensions than neurophysins-I and -III and can be separated from these by gel filtration on Sephadex G-75. It contains no histidine or methionine, and its minimum molecular weight has been estimated as 14020 by amino acid analysis. 7. Each of the three neurophysins possesses N-terminal alanine. 8. The possible biological significance of the existence of several neurophysins within one species is discussed.

Studies on the chemical modification of the tyrosine residue in bovine neurophysin-II

1. Bovine neurophysin-II contains 1mol of tyrosine residue/10000g of protein. This residue could be readily nitrated with tetranitromethane. On hydrolysis and amino acid analysis 1mol of 3-nitrotyrosine was found/10000g of protein. Starchgel electrophoresis at pH8.5 showed that nitration had converted the native protein into a single, more acidic species. The increase in acidity was consistent with the observed fall in pK of the tyrosine hydroxyl from 9.2 in native neurophysin to 7.3 in the nitrated protein. Further, the absence of any intermediate species, even under conditions of minimum substitution, confirmed that the molecular weight of the monomer is 10000. 2. O-Acetylation of the tyrosine residue was carried out with N-acetylimidazole, in conjunction with the reversible blocking of amino groups by citraconylation. The degree of O-acetylation, determined spectroscopically, was 0.9mol of O-acetyltyrosine/10000g of protein. 3. The hormone-binding ability of modified protein was tested by equilibrium dialysis and was found to be unchanged by either nitration or O-acetylation of the tyrosine residue. 4. Interaction of neurophysin-II and [8-arginine]-vasopressin gave rise to a characteristic difference spectrum with a peak at 286.8nm and shoulder at 279.6nm. Part of this hyperchromicity is thought to result from entry of the tyrosine residue at position 2 in the hormone into the hydrophobic environment of the binding site. With nitrated neurophysin-II a second peak appeared at 436nm, showing that the tyrosine of the protein is also perturbed. The very large red shift (84nm) in this region suggests that the 3-nitrotyrosyl residue not only enters a more hydrophobic environment on protein-hormone interaction, but is caused to ionize more fully by the approach of some positively charged group.

Isolation of a third bovine neurophysin

1. A third native hormone-binding protein, neurophysin-C, has been isolated from acetone-desiccated bovine pituitary posterior lobes. 2. This protein was detected in lysates of neurosecretory granules isolated from bovine pituitary posterior lobes. 3. The molecular weight appears to be close to 10000. 4. Neurophysin-C is similar in amino acid composition to neurophysin-I and -II; it contains a single residue of tyrosine and of methionine. The N-terminal amino acid in all three neurophysins is alanine. 5. Neurophysin-C accounts for approximately 15% of the total hormone-binding protein present in the pituitary posterior lobes. 6. The new neurophysin forms complexes with oxytocin as well as with [8-arginine]-vasopressin. The complex with vasopressin has been crystallized. 7. Bioassay of the pressor and oxytocic activities of the protein-hormone complexes shows that neurophysin-C binds one molecule of either vasopressin or oxytocin.

The isolation of the native hormone-binding proteins from bovine pituitary posterior lobes. Crystallization of neurophysin-I and-II as complexes with [8-arginine]-vasopressin

1. The native hormone-binding proteins, neurophysin-I and -II, have been isolated from acetone-desiccated bovine pituitary posterior lobes. 2. Neurophysin-I and -II are present in approximately equal quantities in the tissue and are localized in the neurosecretory granules. 3. The apparent molecular weight, determined by equilibrium sedimentation of neurophysin-I, was 19000 and that of neurophysin-II was 21000; their sedimentation coefficients, S(20,w), were 1.66 and 2.02s respectively. 4. Neurophysin-I and -II are similar in amino acid composition. Neurophysin-II was distinguished from neurophysin-I by the absence of histidine. 5. The proteins form complexes with oxytocin as well as with vasopressin. Complexes of both proteins with [8-arginine]-vasopressin have been crystallized. 6. Bioassay of the pressor and oxytocic activities of the crystals shows that neurophysin-I binds three molecules of either vasopressin or oxytocin whereas neurophysin-II binds only two molecules of each hormone per molecule of protein. Complexes containing two molecules of oxytocin and one molecule of [8-arginine]-vasopressin per molecule of protein are formed by neurophysin-I and -II; both proteins appear to possess three polypeptide-binding sites/molecule.

The isolation of purified neurosecretory granules from bovine pituitary posterior lobes. Comparison of granule protein constituents with those of neurophysin

1. A procedure for the isolation of highly purified neurosecretory granules from the posterior lobe of the bovine pituitary gland is described. The preparation was free from contamination by the mitochondrial enzyme succinate dehydrogenase and the lysosomal enzyme cathepsin. 2. The biological activities of the neurosecretory granules were measured: the oxytocic activity was 11.61+/-1.30units and the pressor activity was 10.73+/-1.74units/mg. of protein. 3. A lysate of the isolated granules was shown to contain two proteins that appear to be identical with two of the constituents of neurophysin. 4. The constituents of neurophysin not present in neurosecretory granules could not be detected in any other subcellular fraction. It is suggested that the components of neurophysin not present in the neurosecretory granules arise as a result of the degradation of the two granular proteins.

Fractionation of neurophysin by molecular-sieve and ion-exchange chromatography

Neurophysin has been separated into seven distinct protein fractions. One of these components had no hormone-binding activity. The fractions that had hormone-binding activity were similar in amino acid composition: their cystine content was in the range 11.5-14.5%. The major component, neurophysin-M, was distinguished from the protein isolated by van Dyke by the presence of methionine and the absence of histidine. Neurophysin-M binds both oxytocin and vasopressin with similar affinities.

The relationship between neurophysin and the soluble proteins of pituitary neurosecretory granules

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