Induction of glycoprotein biosynthesis in activated B lymphocytes

Resting murine splenic B lymphocytes (B cells) can be stimulated to proliferate by exposure to a variety of polyclonal activators. To investigate changes in glycoprotein synthesis that occur during the activation process, N-glycosylation activity was assessed by following the incorporation of [2-3H]mannose into dolichol-linked oligosaccharide intermediates and glycoprotein after B cells were exposed to anti-immunoglobulin M (anti-mu). Stimulation of B cells by anti-mu resulted in a dramatic induction of N-glycosylation activity. The incorporation of radiolabeled mannose into oligosaccharide-lipid increased 9-fold while the rate of labeling of glycoprotein increased 27-fold between 18 and 38 h after exposure to anti-mu. Maximal stimulation of N-glycosylation activity was observed at an anti-mu concentration of 20-50 micrograms/ml. Similar results were obtained when B cells were activated by bacterial lipopolysaccharide (LPS), another polyclonal activating agent. The major dolichol-bound oligosaccharide labeled during the induction period was determined to be Glc3Man9GlcNAc2 by HPLC analysis. Nearly full induction of oligosaccharide-lipid synthesis and protein N-glycosylation was also seen when DNA synthesis was suppressed by activating B cells with anti-mu in a serum-free medium, or by activating with anti-mu or LPS in the presence of hydroxyurea. The results suggest that the N-glycosylation pathway is induced during the G0 to G1 transition or during the G1 period, and that entry into S phase is not required. These studies describe a striking developmental increase in N-glycosylation activity and extend the information on biochemical changes occurring during the activation of B cells.     

Null and electrophoretic mobility mutants in the structural gene for L-lactate dehydrogenase of Saccharomyces cerevisiae

A mutant lacking L-lactate dehydrogenase (EC 1.1.2.3) of Saccharomyces cerevisiae was isolated by its inability to grow on minimal medium with L-lactate as a carbon source. A simple activity gel assay for visualization of this enzyme and the two D-lactate dehydrogenases in this organism (EC 1.1.2.4 and 1.1.1.28) was developed. This enabled us to screen spontaneous and ethylmethanesulfonate-induced back mutants for electrophoretic mobility. Two mutants with a mobility faster than that of the wild type were isolated, and proved to be allelic to the L-lactate dehydrogenase negative mutant.     

The hydroxylation of phenylalanine and tyrosine: a comparison with salicylate and tryptophan.

The hydroxylation of phenylalanine by the Fenton reaction and gamma-radiolysis yields 2-hydroxy-, 3-hydroxy-, and 4-hydroxyphenylalanine (tyrosine), while the hydroxylation of tyrosine results in 2,3- and 3,4-dihydroxyphenylalanine (dopa). Yields are determined as a function of pH and the presence or absence of oxidants. During gamma-radiolysis and the Fenton reaction the same hydroxylated products are formed. The final product distribution depends on the rate of the oxidation of the hydroxyl radical adducts (hydroxycyclohexadiene radicals) relative to the competing dimerization reactions. The pH profiles for the hydroxylations of phenylalanine and tyrosine show a maximum at pH 5.5 and a minimum around pH 8. The lack of hydroxylated products around near pH 8 is due to the rapid oxidation of dopa to melanin. The relative abilities of iron chelates (HLFe(II) and HLFe(III) to promote hydroxyl radical formation from hydrogen peroxide are nitrilotriacetate (nta) greater than ethylenediaminediacetate (edda) much greater than hydroxyethylethylenediaminetriacetate greater than citrate greater than ethylenediaminetetraacetate greater than diethylenetriaminepentaacetate greater than adenosine 5'-triphosphate greater than pyrophosphate greater than adenosine 5'-diphosphate greater than adenosine 5'-monophosphate. The high activity of iron-nta and -edda chelates is explained by postulating the formation of a ternary Fe(III)-L-dopa complex in which dopa reduces Fe(III). The hydroxylations of phenylalanine and tyrosine are similar to that of salicylate (Z. Maskos, J. D. Rush, and W. H. Koppenol, 1990, Free Radical Biol. Med. 8, 153-162) and tryptophan (preceding paper) in that oxidants augment the formation of hydroxylated products by catalyzing the dismutation of hydroxyl radical adducts to the parent compound and a stable hydroxylated product. A comparison of salicylate and the amino acids tryptophan, phenylalanine, and tyrosine clearly shows that salicylate is the best indicator of hydroxyl radical production.     

Ovalbumin-like immunoreactivity detected in chicken sensory neurons by antibodies to aldehyde-treated ovalbumin

Summary A method has been developed to raise an antiserum against ovalbumin that can detect this antigen immunohistochemically in chicken sensory ganglia. Ovalbumin-like immunoreactivity has been identified in a subpopulation of chicken dorsal root ganglion neurons by the generation of antibodies to aldehyde-conjugated ovalbumin but not by the antibodies to native ovalbumin, although both antibodies recognize the much higher concentrations of ovalbumin in sections of the oviduct. Biochemical analysis demonstrated that the antigen is more readily detectable in fixed tissue extracts than in fresh tissue extracts. Sensitive immunoblot analysis combined with affinity purification of the antigen, has confirmed that the antigen is of the same molecular weight as ovalbumin. Furthermore, the immunoreactive material elutes at a position identical to native ovalbumin on a molecular sieve column. These findings argue that molecules sensitive to aldehyde fixation may be more readily detected by the use of antisera prepared against aldehyde-modified antigens. The function of the ovalbumin-like antigen in these neurons is unknown.     

Serum concentrations of deoxycorticosterone in women during the luteal phase of the ovarian cycle are not suppressed by dexamethasone treatment

We determined the serum levels of deoxycorticosterone (DOC) in plasma of six healthy, apparently ovulatory women during the mid-follicular and mid-luteal phases of their ovarian cycles; and we evaluated the effect of dexamethasone (1 mg by mouth) on the concentrations of DOC and cortisol in serum at times when plasma progesterone levels were high or low. The serum levels of DOC, unlike those of cortisol, did not vary significantly in single blood samples obtained in the morning (8-10 a.m.) and afternoon (3-5 p.m.); and serum DOC levels in women were significantly higher (P less than 0.05) during the mid-luteal phase than during the mid-follicular phase of the cycle. There were unmistakable diurnal variations in serum levels of cortisol, and cortisol concentrations were reduced to less than 20% of pretreatment levels after the ingestion of 1 mg dexamethasone during the mid-follicular or mid-luteal phase. The serum concentrations of DOC were reduced only to approx 70% of pretreatment levels after dexamethasone ingestion during the follicular phase. The serum levels of DOC did not decline significantly after administration of dexamethasone during the mid-luteal phase, when progesterone levels in serum are high (14-16 ng/ml). Blood samples also were obtained at hourly intervals during the 24 h before and after dexamethasone administration in one woman during the follicular phase and in another woman the during the early luteal phase (progesterone levels = 1-3 ng/ml) of the ovarian cycle. DOC levels (pre-dexamethasone) fluctuated in synchrony with those of cortisol in the woman studied during the follicular phase but not in the woman studied during the early luteal phase of the cycle. In the post-dexamethasone period, plasma cortisol levels were suppressed for at least 24 h in both women whereas DOC levels were decreased only partially. We conclude that plasma DOC is derived from both adrenal secretion and from extraadrenal 21-hydroxylation of progesterone--the latter source of DOC is not affected by dexamethasone suppression of ACTH secretion.     

A ciliary neuronotrophic factor from peripheral nerve and smooth muscle which is not retrogradely transported

We have found that a CNTF-like molecule which supports ciliary and sympathetic neurons is not retrogradely transported in either sympathetic or parasympathetic nerves. The factor has an apparent M_r of 21 kDa, a pI of 4.9, and is present in peripheral nerves and smooth muscle of the chick. Our experiments indicate that CNTF-like activity does not accumulate on the distal side of ligated chickexpansor nerves. In contrast, there is a clear accumulation of NGF. The activity further differs from NGF in that it is not removed from a smooth muscle of the chick wing by innervating sympathetic fibers. Transection of these fibers does not lead to an accumulation of ciliary activity in theexpansor secundariorum muscle, suggesting that neurons do not actively deplete the muscle of factor by retrograde transport. Finally, recombinant CNTF or semi-purified preparations of CNTF-like activity labelled with¹²⁵I were not transported to the ciliary ganglion of chicks following injection of biologically active material into the eye. Our results suggest either that endogenous CNTF does not act as a survival factorin vivo, or that retrograde transport is not a property inherent to all neuronotrophic molecules.Special issue dedicated to Dr. Lawrence Austin     

16,16 Dimethyl prostaglandin E2 decreases the formation of collagen in fibrotic rat liver slices

The effect of 16,16 dimethyl prostaglandin E2 (DMPG) on fibrogenesis was studied in slices from normal and fibrotic rat liver. Rats received a cirrhogenic diet for seven months; supplemented controls received a diet with the deficient nutrients restored. Slices from fibrotic livers incorporated more 14C-proline and produced more 14C-hydroxyproline in TCA precipitable proteins than slices from control livers. DMPG (10(-10) M) decreased the incorporation of labeled proline and the synthesis of labeled hydroxyproline in slices from fibrotic livers to the same extent, suggesting that DMPG did not affect the hydroxylation of proline per se. The magnitude of the DMPG induced decrease in labeled proline incorporation correlated with the hydroxyproline content in the liver (i.e. with increasing fibrosis there was a greater effect of DMPG: while in control rat liver slices, DMPG had no effect). DMPG did not change the size of the proline pool, its specific activity, or the activity of proline oxidase. We conclude that under these conditions of enhanced fibrogenesis, DMPG decreases the formation of collagen in vitro, possibly by lowering the incorporation of proline into collagen precursors. This may explain, at least in part, the inhibition of fibrogenesis by DMPG in vivo.