Comparison of the Molecular Forms of the Kex2/Subtilisin-Like Serine Proteases SPC2, SPC3, and Furin in Neuroendocrine Secretory Vesicles Reveals Differences in Carboxyl-Terminus Truncation and Membrane Association

Abstract: The molecular forms and membrane association of SPC2, SPC3, and furin were investigated in neuroendocrine secretory vesicles from the anterior, intermediate, and neural lobes of bovine pituitary and bovine adrenal medulla. The major immunoreactive form of SPC2 was the full-length enzyme with a molecular mass of 64 kDa. The major immunoreactive form of SPC3 was truncated at the carboxyl terminus and had a molecular mass of 64 kDa. Full-length 86-kDa SPC3 with an intact carboxyl terminus was found only in bovine chromaffin granules. Immunoreactive furin was also detected in secretory vesicles. The molecular masses of 80 and 76 kDa were consistent with carboxyl-terminal truncation of furin to remove the transmembrane domain. All three enzymes were distributed between the soluble and membrane fractions of secretory vesicles although the degree of membrane association was tissue specific and, in the case of SPC3, dependent on the molecular form of the enzyme. Significant amounts of membrane-associated and soluble forms of SPC2, SPC3, and furin were found in pituitary secretory vesicles, whereas the majority of the immunoreactivity in chromaffin granules was membrane associated. More detailed analyses of chromaffin granule membranes revealed that 86-kDa SPC3 was more tightly associated with the membrane fraction than the carboxyl terminus-truncated 64-kDa form.     

A serotype-specific epitope of dengue virus 1 identified by phage displayed random peptide library

Abstract From a panel of monoclonal antibodies of dengue viruses, a serotype-specific epitope of dengue virus 1 was screened from a random peptide library displayed on phage. The epitope was the determinant reactive with monoclonal antibody 15F3-1 that was specific to dengue 1. The screening was monitored by a dot blotting procedure, and after three rounds of screening a consensus motif, HRYSWK, was found. This sequence matches the sequence HKYSWK, corresponding to the amino acid residues 885–890 of polyprotein or residues 111–116 of the non-structural protein 1 of dengue virus serotype 1. The linear epitope was confirmed by testing the antigenicity of chemically synthesized 8-branched peptide.     

Specific, water-soluble polypeptides in identified neurons of Aplysia californica.

Application of an ethylene glycol lysis technique to extract water-soluble, low molecular weight polypeptides in Aplysia neurons, was used in conjunction with microgradient gel electrophoresis and micro-isoelectric focusing, to identify unique polypeptides in specific, identified neurons. The polypeptides found in neurons R15, R3-13, R14, and the bag cells were particularly abundant, consistent with the previously suggested neurosecretory role for these cells. Water extraction of the strongly basic polypeptides (pI 10.7) in R3-13 and R14 required an acidic lysis medium.     

beta-Endorphin: structure-activity relationships in the guinea pig ileum and opiate receptor binding assays.

The opiate activities of some derivatives and enzymatic digests of camel and human β-endorphin were determined in the guinea pig ileum and rat brain opiate receptor binding assays. Derivatives of β-endorphins altered within the amino-terminal five residues showed pronounced losses in activity. Anisylation of the C-terminal glutamic acid residue of β_h-endorphin produced only small reductions in activity. Chymotryptic digestion greatly weakened the opiate activities of β_h-endorphin, whereas carboxypeptidase A, tryptic and leucine aminopeptidase digests showed only small losses in potency. The C-terminus of β-endorphin appears to contribute little directly to opiate activity. Amino acid analysis and assay of the leucine aminopeptidase digests suggest that the larger potency of β-endorphin relative to Met-enkephalin may be a consequence of its greater resistance to exopeptidase attack.     

Acceleration of pentobarbital metabolism in tolerant mice induced by pentobarbital pellet implantation

The time course of inductions of N-demethylation and pentobarbital hydroxylation of hepatic drug metabolizing system in continuous pentobarbital administration by pentobarbital pellet implantation in the mouse is presented. The results also demonstrate that hepatic microsomal drug-metabolizing enzymes in the mouse could be induced much faster by a single pentobarbital pellet implantation than by the ordinary parenteral administration technique. The reduction of pentobarbital half-life ($\text{T}\text{1}\text{2}$) in plasma, brain and liver of the animals which had been implanted with a pentobarbital pellet also substantiates the acceleration of pentobarbital metabolism in the mouse by the pellet implantation method. The results show that the $\text{T}\text{1}\text{2}$ of pentobarbital in plasma, brain and liver of pentobarbital pellet implanted groups is only $\text{1}\text{2}\text{,}\text{1}\text{6}\text{and}\text{1}\text{9}$ of that of the placebo control group, respectively. The studies on urinary excretion of pentobarbital and its metabolites also reveals that pentobarbital pellet implantation induced much faster rate of metabolism of pentobarbital in the mouse.     

Changes in the fine structure of the testicular Leydig cells of the seasonally-breeding bat,Myotis adversus

Summary Leydig cells of the bat, Myotis adversus, have been examined by electron microscopy throughout fourteen months. During the breeding season the Leydig cells become hypertrophied and are characterised by prominent areas of agranular endoplasmic reticulum and numerous small, membrane-bound granules. Microperoxisomes are also observed. During the period of testicular regression. Leydig cell size and the number of membrane-bound granules are greatly reduced. Lipid droplets and dense bodies are more numerous.     

Resolution of rat renin substrates by isoelectric focusing.

Pooled plasmas from normal or binephrectomized rats and perfusates of isolated livers were used as sources of renin substrate for isoelectric focusing. After desalting, preliminary fractionation (plasma only), and concentration, the preparations were focused in a pH 3--10 gradient on 20-cm glass plates layered with Sephadex slurry. The pH 4--6 region, containing all the substrate, was scraped from this plate and refocused in a pH 4--6 gradient. Substrate content of 1-cm strips of slurry from half of the plate was determined by both radioimmunoassay and bioassay of angiotensin resulting from incubation with added renin. Corresponding strips from the other half of the plate were incubated without renin as a control for any preformed angiotensin. The asymmetry and broad distribution (pH 4--5) of substrate from different sources suggested the existence of more than one form. Higher resolution achieved by using the high substrate concentration of postnephrectomy plasma and 0.5-cm strips of slurry on 20-cm or 40-cm plates revealed peaks and shoulders of substrate activity. Our data suggest that multiple forms of substrate are synthesized by the liver and circulate in plasma. Postnephrectomy rat plasma appears to contain relatively more substrate(s) with higher isoelectric points than in normal plasma, possibly an accumulation of forms ordinarily degraded by endogenous renal renin.     

Activation and measurement of plasma prorenin in the rat.

Prorenin determination in rat plasma has been problematic from the outset. Consequently, its existence is questioned by some and its quantity by others, making it difficult for knowledge to advance as to its function relative to the renin system. The present study examines major variables in the determination of rat plasma prorenin and renin, notably different prorenin activation protocols involving blood samples obtained under various conditions from animals under different anesthetics. We found that a trypsin activation step with 5 mg/mL plasma, 60 min at 23 degrees C, followed by a PRA step of 10 min at 37 degrees C, resulted in the highest prorenin estimates, up to approximately 400 ng.mL-1.h-1 in terms of angiotensin I, as compared with published values of 0-190, based on other protocols. These estimates were obtained despite considerable destruction of angiotensinogen (renin substrate) by trypsin. Cryoactivation of prorenin was much less effective than in human plasma but, when followed by trypsin, it facilitated greater activation than with trypsin alone. Comparable fresh and fresh-frozen plasmas had similar prorenin-renin values, but lower values were observed in plasmas that had been repeatedly frozen and thawed. Conscious rats and those anesthetized with Inactin or ether had higher renins and prorenins than those anesthetized with methoxyflurane or halothane. Rats with kidneys in place during blood collection had higher renins (but not prorenins) than those whose kidneys were clamped off, suggesting that last-minute renin release during blood collection had occurred. We conclude that (i) trypsin generates increased renin, or renin-like, activity in plasma, suggesting activation of a precursor; (ii) on this basis, high prorenin levels exist in normal rat plasma; (iii) renin and prorenin levels are variously influenced by different anesthetics and blood handling procedures; (iv) variation in prorenin levels suggests that it is a dynamic (functional?) component of the renin system; (v) prorenin measurements are heavily influenced by methodological variations during the trypsin step or the subsequent PRA step; (vi) using standardized methodology, the rat can serve as a model for investigating the function of prorenin in normotension and hypertension.     

Specific reduction of delta-opioid receptor binding in transfected NG108-15 cells.

We have recently identified and sequenced the cDNA for an opioid-binding protein with homologies to cell adhesion molecules (OBCAM) (Schofield, P. R., McFarlard, K. C., Hayflick, J. S., Wilcox, J. N., Cho, T. M., Roy, S., Lee, N. M., Loh, H. H., and Seeburg, P. H. (1989) EMBO J. 8, 489-495). Several lines of evidence using antibodies suggest that OBCAM may play a functional role in NG108-15 neuroblastoma x glioma cells, a useful model system that contains a homogeneous population of delta-opioid receptors. A logical extension of this research is to further test this hypothesis. As part of this study, NG108-15 cells were stably transfected with either sense or antisense sequences of a portion of pROM, the rat cDNA for OBCAM. [3H] Diprenorphine binding was greatly reduced in antisense-transfected cells relative to non-transfected cells. Binding to alpha 2-adrenergic, muscarinic, and insulin receptors was unaffected. These results further support the notion that OBCAM or its analogue is part (or a subunit) of an opioid receptor. Furthermore, our observation of an apparently specific reduction in opioid binding in these transfected cells suggests that they may provide a novel genetic approach for studying regulation of the opioid receptor in this defined cell line.     

Requirement of ADP-ribosylation for the pertussis toxin-induced alteration in electrophoretic mobility of G-proteins.

Pertussis toxin (PTX) catalyzes the ADP-ribosylation of the alpha-subunit of GTP-binding proteins (G-proteins) in the presence of NAD+. Pertussis toxin also decreases the electrophoretic mobility of the alpha-subunit on urea SDS PAGE. This effect of PTX has been suggested to be a property of the toxin different from its ability to catalyze ADP-ribosylation. However, the present report provides evidence to the contrary; ie, this mobility shift required the ADP-ribosylation of alpha-subunits. This conclusion was based on: (1) in the presence of increasing concentrations of NAD+ (0.026-1.3 microM), there was a linear increase in the formation of the slower migrating alpha-subunit as measured by immunoblotting with selective antisera, (2) addition of NADase to the incubation mixture completely eliminated the formation of this protein, and (3) increasing concentrations of nicotinamide (50-250 mM), which inhibits ADP-ribosylation, decreased the amount of the slower migrating alpha-subunit. Thus, in addition to PTX, NAD+ was required for the mobility shift and the slower migrating alpha-subunit is likely the ADP-ribosylated form.