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S Bains

Publications and source records attributed to S Bains.

10 recordsLinked to original sources
PubMed1999

Mechanisms of climate warming at the end of the paleocene

An abrupt episode of global warming marked the end of the Paleocene epoch. Oxygen and carbon isotope records from two widely separated sites support the notion that degassing of biogenic methane hydrate may have been an important factor in altering Earth's climate. The data show evidence for multiple injections of methane, separated by intervals in which the carbon cycle was in stasis. Correlations between the two sites suggest that even these small-scale events were global in nature.

Journal Article↗
PubMed1998

Single amino acid substitutions disrupt tetramer formation in the dihydroneopterin aldolase enzyme of Pneumocystis carinii.

In the opportunistic pathogen Pneumocystis carinii, dihydroneopterin aldolase function is expressed as the N-terminal portion of the multifunctional folic acid synthesis protein (Fas). This region encompasses two domains, FasA and FasB, which are 27% amino acid identical. FasA and FasB also share significant amino acid sequence similarity with bacterial dihydroneopterin aldolases. In the present study, this enzyme function has been overproduced as an independent monofunctional activity in Escherichia coli. Recombinant FasAB-Met23 (amino acids 23-290 of the predicted open reading frame) was purified and shown to contain dihydroneopterin aldolase activity. The native FasAB-Met23 is a tetramer of the 30-kDa subunit, demonstrating characteristics of an associating-dissociating equilibrium system in which only the multimeric form of the enzyme is active. Multiple sequence alignment of FasA and FasB with other dihydroneopterin aldolases highlights only three positions where the amino acid is invariable between all the predicted proteins. The role of these conserved amino acid residues in enzyme function was investigated using site-directed mutagenesis. Mutant FasAB-Met23 species were overproduced and purified to near homogeneity. Three FasA domain mutants and two FasB domain mutants had little or no detectable dihydroneopterin aldolase activity, implicating both FasA and FasB in the catalytic mechanism. We show that each mutant protein containing an inactivating amino acid substitution has lost its ability to form stable tetramers.

Aldehyde-Lyases↗
PubMed1998

Conserved in vivo phosphorylation of calnexin at casein kinase II sites as well as a protein kinase C/proline-directed kinase site.

Calnexin is a lectin-like chaperone of the endoplasmic reticulum (ER) that couples temporally and spatially N-linked oligosaccharide modifications with the productive folding of newly synthesized glycoproteins. Calnexin was originally identified as a major type I integral membrane protein substrate of kinase(s) associated with the ER. Casein kinase II (CK2) was subsequently identified as an ER-associated kinase responsible for the in vitro phosphorylation of calnexin in microsomes (Ou, W-J., Thomas, D. Y., Bell, A. W., and Bergeron, J. J. M. (1992) J. Biol. Chem. 267, 23789-23796). We now report on the in vivo sites of calnexin phosphorylation. After 32PO4 labeling of HepG2 and Madin-Darby canine kidney cells, immunoprecipitated calnexin was phosphorylated exclusively on serine residues. Using nonradiolabeled cells, we subjected calnexin immunoprecipitates to in gel tryptic digestion followed by nanoelectrospray mass spectrometry employing selective scans specific for detection of phosphorylated fragments. Mass analyses identified three phosphorylated sites in calnexin from either HepG2 or Madin-Darby canine kidney cells. The three sites were localized to the more carboxyl-terminal half of the cytosolic domain: S534DAE (CK2 motif), S544QEE (CK2 motif), and S563PR. We conclude that CK2 is a kinase that phosphorylates calnexin in vivo as well as in microsomes in vitro. Another yet to be identified kinase (protein kinase C and/or proline-directed kinase) is directed toward the most COOH-terminal serine residue. Elucidation of the signaling cascade responsible for calnexin phosphorylation at these sites in vivo may define a novel regulatory function for calnexin in cargo folding and transport to the ER exit sites.

Amino Acid Sequence↗
PubMed1997

Creating a supportive environment for Indo-Canadian women.

For Indo-Canadian women, pregnancy and delivery can be very difficult because of the women's lack of knowledge of Western medical procedures and techniques. Young women who have recently immigrated are particularly likely to experience some trauma, for their lack of information is compounded by a lack of social support. Many of these young women have immigrated to enter into an arranged marriage, where the husband and his family are relative strangers. When the young woman becomes pregnant, she may experience considerable stress because of the adjustments she is required to make-to a new language, culture, husband and in-law family as well as to the physical changes associated with pregnancy. Her situation is also significantly affected by the traditional role of the young wife in Indian culture: As the junior woman in the family, she has the lowest status.

Canada↗
PubMed1994

The mouse t-complex gene, Tcp-11, is under translational control.

The mouse t-complex is known to harbour genes which affect male fertility. Tcp-11 is a t-complex gene which is only expressed in male germ cells and from its position is a candidate for a distorter, one of the two types of genetic element involved in transmission ratio distortion. Antibodies raised to TCP-11 protein made in E. Coli were used on thin sections of testis and shown to recognise late spermatids. On Western blots the antibodies bound to a 68-kD protein present in protein extracts from testis. No specific signal could be detected using the antibody on protein extracts from other mouse tissues. Following gentle lysis of the germ cells and fractionation on sucrose gradients, all the material recognised by the anti-Tcp-11 antibody was found to be soluble and unassociated with any membrane fraction or organelle. A comparison of the time course of expression of the Tcp-11 mRNA and the TCP-11 protein revealed that expression of this gene is under translational control.

Animals↗
PubMed1994

Restricted expression of a zinc finger protein in male germ cells.

Zfp-37 is a zinc finger protein gene expressed in male germ cells. The cDNA detected two transcripts on Northern blots of testis RNA, with expression first detected at around day 19. To establish the pattern of expression of the protein we have raised antibodies to ZFP-37 and used them on thin sections of testis and on Western blots. On Western blots the antibody detected two proteins exclusively in testis extracts, confirming the previous mRNA expression data. A time-course study revealed that the larger of the two proteins appears at about day 22 but the smaller one is not detected until day 34. Analysis of the expression of these two proteins in purified germ cell preparations revealed that the smaller protein is only detectable in the elongating spermatids or residual bodies. Data from thin sections showed that most, but not all, of the protein recognized by the antibody is in the nucleus, a result further confirmed by Western blotting. These results are discussed in the light of the possible role of this protein in regulating spermatogenesis.

Animals↗
PubMed1987

Inverse relationship between cytochrome P-450 phosphorylation and complexation with cytochrome b5.

Cytochrome P-450 LM2 purified from rabbit liver microsomes has been shown to be a substrate for cAMP-dependent protein kinase. Cytochrome b5, in contrast, was a very poor substrate for cAMP-dependent protein kinase, although it stimulated the activity of the kinase toward histone. When purified rabbit cytochrome b5 was mixed with purified LM2, phosphorylation of LM2 by cAMP-dependent protein kinase was inhibited approximately 80-90%. Recently, a functional covalent complex of cytochrome b5 and LM2 was prepared and purified to homogeneity (P.P. Tamburini and J.B. Schenkman (1987) Proc. Natl. Acad. Sci. USA 84, 11-15). When present as a covalent complex with cytochrome b5, the phosphorylation of LM2 in the complex by cAMP-dependent protein kinase was also inhibited about 80-90% relative to an equivalent amount of LM2 alone. On the other hand, when the LM2 was phosphorylated prior to interaction with cytochrome b5, the ability of the latter to perturb the spin equilibrium of LM2 and oxidation of p-nitroanisole by the LM2 was diminished to an extent comparable to the degree of phosphorylation. The results suggest either that the phosphorylation site on LM2 may be within the cytochrome b5 binding site or that phosphorylation and cytochrome b5 cause mutually exclusive conformational changes in LM2. In addition, eight different forms of cytochrome P-450 from the rat (RLM2, RLM3, fRLM4, RLM5, RLM5a, RLM5b, RLM6, and PBRLM5) were examined as potential substrates for cAMP-dependent protein kinase under the same conditions. Maximal phosphorylation of about 20 mol% was obtained with LM2, and about half as much with PBRLM5. The low extent of phosphorylation of LM2 was not due to the prior presence of phosphate on the enzyme since LM2, as isolated, contains less than 0.1 mol phosphate/mol of enzyme. The other forms of cytochrome P-450 tested showed little or no phosphorylation in vitro despite the presence of a cAMP-dependent protein kinase phosphorylation sequence on at least two of them.

Animals↗