Studies on the primary structure and biological activity of a human neurophysin

mRNA sequence predictions from homologous protein sequences

A model has been developed that permits the prediction of mRNA nucleic acid sequence from the sequences of the translated proteins. The model relies on the information obtained from the comparison of protein sequences in related species to reduce the number of possible codons for those amino acids where mutations are observed. The predictions so obtained have been tested by applying the model to proteins whose mRNA sequences are known. The model's predictions have been found to be 100% accurate if three or more different amino acids are known at a given position and if the protein sequences are restricted to relatively closely related species (within the same class). The use of this model may permit a reduction of the mRNA sequence degeneracy and therefore be helpful in the synthesis of cDNA probes or for the prediction of restriction endonuclease sites. Computer programs have been developed to ease the use of the model.

Immunohistochemical characterization of intracellular J-chain and binding site for secretory component (SC) in human immunoglobulin (Ig)-producing cells

J-chain staining of IgA- and IgM-producing immunocytes was significantly enhanced when tissue sections were pretreated with acid urea, apparently because molecular unfolding exposed concealed J-chains. This indicated substantial completion of the Ig polymers at the cytoplasmic level, which was verified by diffuse binding of SC in vitro to the cytoplasm of most J-chain-positive IgA and IgM cells. This process involved specific non-covalent forces which showed the same interrelation as that noted for isolated dimeric IgA and 19S IgM--the latter as well as IgM cells exhibiting stronger binding of SC than the IgA counterparts. Conversely, J-chain staining of IgD and IgG immunocytes was not enhanced by acid urea and these cells did not generally express affinity for SC; rare exceptions could apparently be ascribed to artifacts or dual isotype production including IgA or IgM polymers. Parallel demonstration of J-chain and SC binding seems to be the best available method for studies of polymer-producing immunocyte populations and offers the advantage of in situ evaluation of cell distribution in relation to morphology. The reliability of this approach was attested to by the fact that IgA immunocytes in all secretory tissues investigated (salivary, mammary and lacrimal glands; nasal and intestinal mucosae) expressed J-chain (87-97%) and SC affinity (84-87%) in comparable proportions, indicating that almost 90% of the cells were engaged mainly in dimer production. The observation that most IgD and 50-70% of the IgG immunocytes in secretory tissues expressed J-chain, has implications for the differentiation of B-cell clones homing to such sites. Conversely, IgG cells in extra-glandular tissues showed strikingly reduced J-chain production and such sites contained IgA immunocytes with heterogeneous expression of J-chain and SC affinity. Thus, in the extra-follicular area of palatine tonsils 70-80% of the IgA cells seemed to be pure monomer producers and the remainders apparently generated a mixed product. Most immunocytes in extra-glandular tissues may therefore belong to mature clones with completely or partially repressed J-chain synthesis.

Identification of human neurophysins: complete amino acid sequences of MSEL- and VLDV-neurophysins

Two human neurophysins have been purified from acetone-desiccated posterior pituitaries by acidic extraction, molecular sieving, and ion-exchange chromatography. The complete amino acid sequence of each protein has been determined by using a sequencer and characterizing two sets of overlapping enzymic peptides. The two neurophysins belong to two structural families previously defined as MSEL- and VLDV-neurophysins according to the nature of the residues in positions 2, 3, 6, and 7. (MSEL-neurophysins contain methionine-2, serine-3, glutamic acid-6, and leucine-7; VLDV-neurophysins contain valine-2, leucine-3, aspartic acid-6, and valine-7.) Human MSEL-neurophysin has only 93 residues instead of 95 usually found in MSEL-neurophysins from other mammalian species, probably because of a deletion of amino acids 91 and 92. Compared with bovine MSEL-neurophysin, nine variations (seven substitutions and two deletions) are observed. Human VLDV-neurophysin has 93 residues, as do the other mammalian VLDV-neurophysins. There are 11 substitutions when the comparison is made with bovine VLDV-neurophysin. Between the two human neurophysins, there are 26 variations. However, the central parts of the proteins (residues 10-70) are nearly identical. Furthermore, in this region identical substitutions are found in positions 29 and 60 of both neurophysins, suggesting either a single exon or some relationship between the two corresponding genes.

Nature of the immunoreactive neurophysins in ectopic vasopressin-producing oat cell carcinomas of the lung. Demonstration of a putative common precursor to vasopressin and neurophysin

In an attempt to delineate the nature of the immunoreactive neurophysins in oat cell carcinomas of the lung with ectopic vasopressin production, tumor neurophysins were characterized by gel filtration and by electrophoresis. In all of the five tumor tissues, activities of both vasopressin and nicotine-stimulated neurophysin (NSN) determined by radioimmunoassay were demonstrated. A small amount of oxytocin as well as estrogen-stimulated neurophysin was detected in three of the tissues. When tissue extract was subjected to Sephadex G-50 gel filtration in 0.2 N acetic acid, the major portion of immunoreactive NSN emerged in the fractions corresponding to the molecular size of 10,000. The migration pattern of NSN in these fractions on electrophoresis was qualitatively the same as that of NSN extracted from human posterior pituitary glands. In addition to this major neurophysin, immunoreactive NSN with the molecular size of 20,000 was consistently demonstrated in three tumor extracts. This high molecular weight form of neurophysin represented 6.5--8.7% of total NSN immunoactivities in each tumor extract and its elution profile was not changed when analyzed under denaturating conditions in 6 M guanidine hydrochloride. On electrophoresis, it migrated near the gamma globulin region; however, the peak was broad suggesting that it consists of more than two different molecular populations. A substantial portion of the high molecular weight NSN appears to be a glycoprotein judging from its binding to concanavalin A. When the high molecular weight from of neurophysin was incubated with trypsin, essentially all of the activities were converted into NSN with the molecular size of 10,000. Moreover, an equimolar amount of vasopressin was liberated after the treatment, the elution pattern of which closely resembled that of synthetic arginine vasopressin. When a lower concentration of trypsin was used, some of the 20,000-dalton neurophysin exhibited activities of both NSN and vasopressin. Since the antivasopressin serum used in this study appeared to be directed toward the ring portion side of vasopressin, these results suggest that this 20,000-dalton neurophysin is, in all probability, a common precursor to vasopressin and neurophysin, and that vasopressin may be located in the middle of the precursor molecule.

Purification of porcine neurophysins I and II by high performance liquid chromatography

Porcine neurophysins I and II have been reported to be metabolically active. This activity was suggested to be due to contaminations. Furthermore, neurophysin I has been suggested to be heterogeneous on the basis of amino acid sequence analysis. The neurophysins I and II were isolated from porcine pituitary glands. Though they seemed homogeneous in polyacrylamide gel- and sodium dodecyl sulfate electrophoresis, neurophysin I could be separated into neurophysin I1 and I2 by high performance liquid chromatography. Neurophysin I2 differs from neurophysin I1 by one additional C-terminal amino acid. The purified neurophysins had no metabolic activity.