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Biomedical subjects

R K Gupta

Publications and source records attributed to R K Gupta.

At least 703 records · Page 39Linked to original sources
PubMed1980

Noninvasive 31P NMR probes of free Mg2+, MgATP, and MgADP in intact Ehrlich ascites tumor cells.

(31)P NMR spectra of Ehrlich ascites tumor cells, suspended in a physiological medium, show well-defined alphaP, betaP, and gammaP resonances of intracellular ATP. A comparison of the separation of 360 +/- 1 Hz between the resonances of alphaP and betaP in intact cells with the corresponding separations of 349 +/- 0.5 and 438 +/- 1 Hz in noncellular MgATP and ATP standards, measured at 10 degrees C and 40.5 MHz NMR frequency, reveals that 88% of the total intracellular ATP (3.3 mM) is complexed to Mg(2+). The corresponding value for intracellular free Mg(2+) is 0.44 mumol/ml out of a total Mg(2+) content of 8.5 mumol/ml cell water. A similar value of free Mg(2+) is obtained from a comparison of the separation of 560 +/- 1 Hz between the betaP and gammaP resonances of intracellular ATP with the corresponding values of 552 +/- 0.5 and 621 +/- 1 Hz in noncellular MgATP and ATP standards. The fraction of total cellular ATP complexed to Mg(2+) decreased to 80% in tumor cells incubated in a medium containing adenosine, glucose, and P(i) without Mg(2+), the corresponding level of intracellular free Mg(2+) being significantly lower (0.24 mM) than that in the unincubated cells. With Mg(2+) present in the incubation medium, MgATP and total Mg(2+) levels increased by approximately 2.5 mM, whereas with no added Mg(2+), the MgATP increased 1.6 mM apparently at the expense of other Mg(2+)-complexed constituents since total Mg(2+) remained essentially unchanged. At the measured levels of free Mg(2+), intracellular ADP will be only 35-50% complexed to Mg(2+). A knowledge of the state of Mg(2+) complexation of ATP and ADP in intact Ehrlich tumor cells allows an accurate estimation of the phosphorylation potential and the extent of deviation of the mass action ratio ([MgATP][AMP](f)/[MgADP][ADP](f)) in cells with high phosphorylation potential from the Mg(2+)-dependent equilibrium value of the adenylate kinase reaction. The significance of the free Mg(2+) value measured by the noninvasive NMR method in relation to the existence of Mg(2+) complexation and compartmentation in tumor cells is discussed.

Adenosine↗
PubMed1980

Natural humoral immunity in patients with malignant disease.

In order to assess the association of enhancement or suppression of humoral immune responses with cancer histology, sera from age and sex matched patients with sarcoma, melanoma and breast cancer and from normal donors were tested for natural antibodies in six serologic assays. Patients with melanoma were found to have a significantly higher level of antibody than the other groups tested. Antibody levels in patients with breast cancer were lowest.

Adult↗
PubMed1979

A novel form of vitamin B-12 and its derivatives.

A new isomeric form of cobalamins is reported. The conversion of cobalamin to cobalamin (the new form) is achieved by substituting the benzimidazole base by a less bulky group like H2O or CN- and modest thermal treatment. The back conversion of adenosylcobalamin to the corresponding regular form occurs in the "base-off" form at room temperature. It seems that the corrin ring becomes quite flexible in the "base-off" form and the freer axial movement of the cobalt atom flips the corrin ring into a different conformation. The change in conformation is borne out by subtle changes in the proton magnetic resonances on the corrin ring and the base, and very marked variation in the emission Mössbauer spectra. The latter is indicative of appreciable changes in the spatial conformation in the immediate vicinity of the central metal atom. The ultraviolet-visible and infrared spectra of cobalamin are indistinguishable from those of its corresponding regular form. The new conformational isomeric species is present as an impurity in all commercially available cobalamins (including pharmaceutical preparations). It raises the question whether the cobalamins' constitute the real biologically active anti-anemic factor in humans.

Anemia↗
PubMed1979

Proton nuclear magnetic resonance study of cobrotoxin.

Cobrotoxin (Mr 6949), which binds tightly to the acetylcholine receptors, contains no phenylalanines and only two histidines, two tyrosines, and one tryptophan that result in well-resolved aromatic proton resonances in D2O at 360 MHz. His-32, Tyr-25, and the Trp are essential for toxicity and may interact with the acetylcholine receptor. We assign two titratable resonances (pKa = 5.1) at delta = 9.0 and 7.5 ppm at pH 2.5 and at 7.7 and 7.1 ppm at pH 9.5 to the C-2 and C-4 ring protons, respectively, of His-4. Two other titratable resonances (pKa = 5.7) at delta = 8.8 and 6.9 ppm at pH 2.5 and at 7.8 and 6.7 ppm at pH 9.5 are assigned to the C-2 and C-4 ring protons of His-32, respectively. The differences in delta values of the two histidines reflect chemically different microenvironments while their low pKa values could arise from nearby positive charges. A methyl resonance gradually shifts upfield to delta approximately 0.4 ppm as His-4 is deprotonated and is tentatively assigned to the methyl group of Thr-14 or Thr-15 which, from published X-ray studies of neurotoxins, are located in the vicinity of His-4. Further, we have identified the aromatic resonances of the invariant tryptophan and individual tyrosines and the methyl resonance of one of the two isoleucines in the molecule. Several broad nontitrating resonances of labile protons which disappear at pH greater than 9 may arise from amide groups of the beta sheet in cobrotoxin.

Amino Acid Sequence↗
PubMed1979

Detection of cancer-associated antigen(s) in urine of sarcoma patients.

Tumor-associated antigens were demonstrated in concentrated and dialyzed urine of several sarcoma patients with large tumor burden. The antigens were detected by complement fixation using autologous and allogeneic sera from sarcoma patients. The antigenic activity in three patients who were studied sequentially disappeared after surgical ablation of tumor. In two of these three patients, the antigenic activity reappeared before tumor recurrence. The reactivity of the sarcoma sera to the urine could be abolished by absorption of the sera with human sarcoma cells but not by normal human liver cells, which indicates that the same antigen was present in the urine and on biopsy-obtained sarcoma cells. Urine from cancer patients with high tumor burden may be useful as a source of tumor-associated antigen. Further studies on the presence of these antigens in urine of sarcoma patients may lead to a method for detecting subclinical tumor recurrence.

Adult↗
PubMed1979

Antigenic similarity between squamous cell carcinoma of horn (horn cancer) and normal bovine foetal tissues.

Normal bovine foetal (liver and skin) and horn cancer tissue antigens were examined using double diffusion agar gel precipitation and immuno-electrophoretic tests to detect any cross reactivity among them. Rabbit horn cancer antisera absorbed with normal bovine liver, skin and horn core epithelium antigens, when tested with foetal skin and liver (4 to 6 months of gestation), revealed the presence of 2 foetal antigens in horn cancer. Immuno-chemically 2 of the horn cancer antigens were found to be identical to the bovine foetal antigens.

Animals↗