Search PubMed⌕ Search

Biomedical subjects

N Nath

Publications and source records attributed to N Nath.

At least 55 records · Page 3Linked to original sources
PubMed1986

Location of the sites of reaction of N-ethylmaleimide in papain and chymotryptic fragments of the gizzard myosin heavy chain.

The thiol of the gizzard myosin heavy chain, which reacts most rapidly with N-ethylmaleimide (MalNEt), has been located in the subfragment 2 region of myosin rod by fragmentation of [14C]-MalNEt-labeled myosin with papain and chymotrypsin. MalNEt reacts more slowly with thiols present in the 70- and 25-kilodalton (kDa) papain fragments of subfragment 1. The reaction of MalNEt with thiols present in these regions is increased on addition of ATP by factors of 2 and 10, respectively, when myosin is modified in 0.45 M NaCl where it is present in the extended, 6S conformation. The rate of increase of Mg2+-activated adenosinetriphosphatase (ATPase) activity, which reflects the loss of ability of myosin to assume the folded, 10S conformation, and the rate of loss of K+-EDTA-activated activity produced by MalNEt are both accelerated 5- to 10-fold on addition of ATP. The rates at which ATPase activities change agree closely to the reaction rates of MalNEt with the 25-kDa region of subfragment 1; therefore, the changes in these activities can be attributed to modification of a thiol of the 25-kDa segment. An increase in actin-activated ATPase activity produced by reaction of myosin with MalNEt in 0.45 M NaCl is accelerated by ATP by a factor of at least 4. Reaction with [14C]MalNEt in the presence of MgATP and 0.2 M NaCl, where myosin is in the 10S form, inhibits the incorporation of radioactive MalNEt into the 25-kDa papain fragment of subfragment 1. It also prevents the increase in actin-activated ATPase activity and preserves the ability of myosin to assume the 10S form.

Adenosine Triphosphatases↗
PubMed1986

Ca2+ dependence of the ATPase activity of phosphorylated smooth muscle myosin: effects of tropomyosin and actin.

Calcium ions produce a 3-4-fold stimulation of the actin-activated ATPase activities of phosphorylated myosin from bovine pulmonary artery or chicken gizzard at 37 degrees C and at physiological ionic strengths, 0.12-0.16 M. Actins from either chicken gizzard or rabbit skeletal muscle stimulate the activity of phosphorylated myosin in a Ca2+-dependent manner, indicating that the Ca2+ sensitivity involves myosin or a protein associated with it. Partial loss of Ca2+ sensitivity upon treatment of phosphorylated gizzard myosin with low concentrations of chymotrypsin and the lack of any change on similar treatment of actin supports the above conclusion. Although both actins enhance ATPase activity, activation by gizzard actin exhibits Ca2+ dependence at higher temperatures or lower ionic strengths than does activation by skeletal muscle actin. The Ca2+ dependence of the activity of phosphorylated heavy meromyosin is about half that of myosin and is affected differently by temperature, ionic strength and Mg2+, being independent of temperature and optimal at lower concentrations of NaCl. Raising the concentration of Mg2+ above 2-3 mM inhibits the activity of heavy meromyosin but stimulates that of myosin, indicating that Mg2+ and Ca2+ activate myosin at different binding sites.

Actins↗
PubMed1986

Hepatitis B virus polypeptide X: expression in Escherichia coli and identification of specific antibodies in sera from hepatitis B virus-infected humans.

Sequence analysis of the hepatitis B virus (HBV) genome revealed the presence of an open reading frame (ORF X) which has the potential to encode a 154-amino acid polypeptide. A fusion protein containing 145 of the amino acids encoded by ORF X and 8 amino acids of beta-galactosidase was expressed and characterized in bacterial extracts. Immunoprecipitations with the ORF X fusion protein as a radioactively labeled antigen were performed to screen sera of humans infected with HBV for the presence of antibodies against ORF X-encoded determinants (anti-X). Such antibodies were identified in 9 samples from a set of 26 sera characterized as positive for HBV surface antigen but were not found in 16 normal human sera. The data reported here demonstrate that sera from some patients with markers of HBV infection contain antibodies directed against the polypeptide encoded by ORF X. As such, these findings represent evidence that ORF X constitutes a gene, or a portion of a gene, which is expressed during HBV infection. Although there does not appear to be a direct relationship between anti-X and any individual markers of HBV infection, our data suggest that anti-X is more prevalent in HBV-positive sera containing antibodies to HBe3 antigen (anti-HBe3).

Base Sequence↗
PubMed1985

Modification of thiols of gizzard myosin alters ATPase activity, stability of myosin filaments, and the 6-10 S conformational transition.

The pattern of incorporation of [14C]N-ethylmaleimide (MalNEt) into gizzard myosin indicates the presence of two classes of thiols: rapidly and slowly modified. The first class contains two thiol residues, SH-A and SH-B, located in the myosin rod and the 17-kDa light chain, respectively, while the second contains at least two thiols located in the myosin heavy chain. Changes in ATPase activities upon modification occur rapidly or slowly, paralleling reaction of either the first or second class of thiols. Rapid changes include increases in the Ca2+- and Mg2+-activated activities of myosin alone, measured at ionic strengths below 0.3 M, and an increase and a decrease in the actin-activated activity of dephosphorylated and phosphorylated myosin, respectively. Modification of SH-A and SH-B with MalNEt is accompanied by stabilization of myosin filaments, seen as an increase in light-scattering intensity, and by destabilization of the folded, 10 S conformation of the myosin monomer. In the presence of 0.175 M NaCl and 1 mM MgATP, unmodified and MalNEt-modified myosin sediment in the ultracentrifuge as single components at 10.0 S and 6.0 S, respectively. The MalNEt-induced increase in the Ca2+- or Mg2+-activated ATPase activity, measured in the absence of actin, can be attributed either to stabilization of filaments or to destabilization of the 10 S conformation, depending on the ionic strength of the assay. Modification of the second class of thiols is accompanied by a decrease in K+-EDTA-activated activity and an increase in Ca2+-activated activity measured above 0.3 M NaCl, where myosin neither forms filaments nor assumes the 10 S conformation. These slow changes are characteristic of blocking the SH-1 thiols of skeletal-muscle myosin, but in gizzard myosin are attributable to modification of a less reactive thiol, SH-C.

Actins↗
PubMed1985

Metabolism of L-ascorbic acid in the prostate of normal and scorbutic guinea pigs.

Guinea pig prostate was found to actively participate in the biosynthesis and catabolism of ascorbic acid. The key ascorbic acid biosynthetic enzyme L-gulono-gamma-lactone oxidase and the other two lactonases were found to be present in guinea pig prostate. The activities of dehydroascorbatase and diketogulonate decarboxylase, the enzymes for ascorbic acid degradation, were also detected in guinea pig prostate. Male guinea pigs kept under scorbutic condition for 7, 14, 21 and 28 days, were examined for prostatic metabolism of ascorbic acid. A significant but gradual decrease in the concentration of L-ascorbic acid was observed in prostate, total blood and leukocytes with the progression of scorbutic condition. There was an appreciable decrease in the rate of lipid peroxidation under the scorbutic condition. In the tissue fraction of scorbutic guinea pigs, the activities of biosynthesizing enzymes, measured in vitro, under optimum conditions were found to be higher with no significant alterations in the catabolizing enzymes. The implications of these findings are discussed in this paper.

Animals↗
PubMed1985

Antibodies to delta antigen in asymptomatic hepatitis B surface antigen-reactive blood donors in the United States and their association with other markers of hepatitis B virus.

A total of 1,915 sera collected in 1979 from asymptomatic hepatitis B surface antigen (HBsAg) carriers were tested for delta antigen, antibody to delta antigen (anti-delta), hepatitis B e antigen (HBeAg) and antibody to hepatitis B e antigen (anti-HBe) in addition to HBsAg and its subtypes. These sera represented blood donated by volunteers to 49 of 57 regions of the American Red Cross located in nine geographic regions of the United States and Puerto Rico. A total of 72 (3.8%) sera had anti-delta activity while none had a detectable level of delta antigen. A significantly higher (p less than 0.01) prevalence of anti-delta (12.1%) was found in San Jose, California (Pacific Region); on the other hand, the East South Central region covering Alabama, Kentucky, Mississippi and Tennessee had a significantly lower (p less than 0.05) prevalence (1.4%) of anti-delta when compared with all other regions combined. Anti-delta was, however, detected in all regions of the United States and in Puerto Rico. The cause of significant differences in the prevalence of anti-delta was not clear. The distribution of anti-delta was not associated with age, sex or blood type of the donor. Sixty-nine of 70 samples with anti-delta were found among the 1,527 samples that had either HBeAg or anti-HBe. And among 149 that lacked both HBeAg and anti-HBe, only one sample had anti-delta. The difference is statistically significant (p less than 0.05). The presence of anti-delta was not associated with HBsAg/ad (2.7%) or HBsAg/ay (4.6%).

Adolescent↗
PubMed1985

Identification of hepatitis B virus polypeptides encoded by the entire pre-s open reading frame.

The open reading frame (ORF) that encodes the 226-amino-acid coat protein (hepatitis B virus surface antigen [HBsAg]) of hepatitis B virus has the potential to encode a 400-amino-acid polypeptide. The entire ORF would direct the synthesis of a polypeptide whose C-terminal amino acids represent HBsAg with an additional 174 amino acids at the N terminus (pre-s). Recently, virus particles have been shown to contain a polypeptide that corresponds to HBsAg with an additional 55 amino acids at the N terminus encoded by the DNA sequence immediately upstream of the HBsAg gene. A novel ORF expression vector containing the TAC promoter, the first eight codons of the gene for beta-galactosidase, and the entire coding sequence for chloramphenicol acetyltransferase was used in bacteria to express determinants of the 174 amino acids predicted from the pre-s portion of the ORF. The resulting tribrid protein containing 108 amino acids encoded by pre-s was expressed as one of the major proteins of bacteria harboring the recombinant plasmid. Single-step purification of the tribrid fusion protein was achieved by fractionation on a chloramphenicol affinity resin. Polyclonal antiserum generated to the fusion protein was capable of detecting 42- and 46-kilodalton polypeptides from virus particles; both polypeptides were also shown to contain HBsAg determinants. The ability of the polyclonal antiserum to identify polypeptides with these characteristics from virus particles presents compelling evidence that the DNA sequence of the entire ORF is expressed as a contiguous polypeptide containing HBsAg. The presence of multiple promoters and primary translation products from this single ORF argues that the function and potential interaction of the encoded polypeptides play a crucial role in the life cycle of the virus. Furthermore, the procedure and vector described in this report can be applied to other systems to facilitate the generation of antibodies to defined determinants and should allow the characterization of the epitope specificity of existing antibodies.

DNA, Recombinant↗
PubMed1985

Effect of castration on the metabolism of L-ascorbic acid in rat prostate.

An appreciable decrease in the contents of prostatic ascorbic acid and dehydroascorbic acid along with an increase in diketogulonic acid was seen in rats ten days after castration. Castration caused a decrease in the activities of such biosynthetic enzymes as L-gulono-gamma-lactone oxidase and D-glucuronolactone-delta-hydrolase with no significant alteration in the activity of L-gulono-gamma-lactone hydrolase in the rat prostate. The activity of dehydroascorbatase, one of the degrading enzymes was, however, found to be elevated in castration. The implication of these results has been discussed.

2,3-Diketogulonic Acid↗
PubMed1984

Superoxide dismutase in diabetic polymorphonuclear leukocytes.

The level of superoxide anion was found to be significantly elevated in polymorphonuclear leukocytes (PMNL) from diabetic subjects as compared with those from normal subjects. This elevation was attributed to the significant reduction in the activities of both cytoplasmic and mitochondrial superoxide dismutase (SOD), the effect being more pronounced in the cytoplasmic fraction. Although the content of copper decreased considerably in the diabetic PMNL, the decrease in the zinc content was less significant, with an insignificant alteration in the content of manganese. PMNL obtained from insulin-treated diabetic patients showed considerable alleviation of SOD levels. The implication of these results are discussed herein.

Adult↗
PubMed1984

Ascorbic acid in thyroidectomized rats. I) Biosynthesis and catabolism.

Thyroidectomized rats showed a decrease in ascorbic acid and dehydroascorbic acid, with almost no alterations in the diketogulonic acid in liver and kidney. Total ascorbic acid in urine was found to be increased, whereas glucuronic acid in urine decreased significantly. There were no significant changes in the activities of ascorbic acid synthesizing enzymes. Activities of the degrading enzymes were found to increase significantly in the liver, with no remarkable change in their activities in kidney. Daily administration of thyroxine for 10 days to thyroidectomized rats normalized the activities of dehydroascorbatase and 2,3 diketoaldonate decarboxylase in the liver, whereas single administration of thyroxine on the 7th day after thyroidectomy could not bring about such restoration. It seems that thyroxine has no direct role on ascorbic acid metabolism in rats.

Animals↗