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Biomedical subjects

R K Gupta

Publications and source records attributed to R K Gupta.

At least 775 records · Page 43Linked to original sources
PubMed1975

Magnetic resonance study of exchangeable protons in human carbonic anhydrases.

A titratable exchangeable proton resonance assignable to a histidine imidazole ring N--H proton is observed approximately minus 15 ppm downfield from tetramethylsilane. The chemical shift of this resonance is affected by sulfonamide and anion inhibitors, and by removal of zinc or replacement of zinc by cobalt, indicating that the proton is located at or near the active site. The pH dependence of the chemical shift of this resonance, which is abolished by inhibitors, reflects the titration of a group with a pK-a of 7.3 in human carbonic anhydrase B and smaller than or equal to 7.1 in human carbonic anhydrase C. These pK-a values are interpreted to be due to the ionization of a neutral imidazole to form the imidazolate anion coordinated to zinc. A mechanism for enzymatic catalysis involving reversible deprotonation and coordination of a histidine to the metal is consistent with these studies.

Amides↗
PubMed1975

Nuclear relaxation studies on human methemoglobin. Observation of cooperativity and alkaline Bohr effect with inositol hexaphosphate.

Ehanced spin-lattice relaxation (1/t1) of water protons induced by the heme iron of human aquomethemoglobin is exchanged-limited (koff = 1.4 times 10-4 per s at 30 degrees, H+ =7.5 Cal per mol) as indicated by the temperature and frequencey dependencies. A comparison of deuteron and proton relaxation rates revealed an order of magnitude primary isotope effect and a small inverse secondary isotope effect on the escape rate of protons from the heme iron into bulk water establishing the exchange of protons and not the exchange of the entire water molecule to be the chemical mechanism of the entire water molecule to be the chemical mechanism of the exchange process. With fluoromethemoglobin, the relaxation rate is in the fast exchange region. The results can be understood in terms of a water molecule interacting with the heme iron at an iron to proton distance less than 3.4 A in aquomethemoglobin and a single proton at a distance of 4.11 A assignable to the NH proton of the distal histidine imidazole group in fluoromethemoglobin. The relaxation rates are pH-dependent and normal titrations with Hill coefficients n = 1 are observed. The pKa is less than or equal to 6. 7 with aquomethemoglobin and 8.5 with fluoromethemoglobin at 30 degrees C. The binding of inositol hexaphosphate in stoichiometric amounts has no significant effect on the magnetic susceptibility of solutions of aquomethemoglobin and fluoromethemoglobin, but in the former case it increases koff to 3.8 times 10-4 per s by lowering the H+ barrier to 6.8 Cal per mol. In fluoromethemoglobin, inositol hexaphosphate decreases the iron to distal histidine NH distance by 0.17 A and the electron relaxation time taus by 10% as determined by the frequency dependence of 1/T1. In the aquomethemoglobin system, inositol hexaphosphate induces a Bohr effect, raising the pKa of the ionization responsible for the 1/T1 titration to 7.2, and induces cooperativity in the pH titration with a Hill coeffocoemt n = 2.8 plus or minus 0.1. With fluoromethemoglobin, the normal pH titration curve is unaffected by inositol hexaphosphate (n approximately equal to 1). Further, relaxivity titrations with varying amounts of azide and fluoride near neutral pH show normal behavior (n = 1) with and without inositol hexaphosphate. These results indicated that inositol hexaphosphate alters the quaternary structure of methemoglobin to the deoxy conformation without causing a change in the spin state of the heme iron...

Binding Sites↗
PubMed1975

Successful transurethral intralesional BCG therapy of a bladder melanoma.

An isolated metastasis of malignant melanoma to the urinary bladder of a patient was sucessfully eradicated by transurethral intralesional injection of BCG. Total destruction of the tumor was confirmed by subsequent excision. Lymphocyte blastogenesis studies revealed no significant alteration in immunocompetence secondary to the therapy, except for an increased responsiveness to PPD. There was no evidence of presence of blocking factors following therapy; cytotoxicity against MLA-14 melanoma cells sharply increased after the intralesional injection. Humoral antimelanoma antibody levels, determined by complement fixation, were decreased before the intralesional therapy, but increased markedly immediately following the transurethral BCG injection.

Antibodies, Neoplasm↗
PubMed1975

Restoration of immunocompetency by lymphocyte transfusion.

A female patient with metastatic osteosarcoma was given a lymphocyte transfusion from her brother, cured of the same histologic type of tumor ten years earlier. Prior to the transfusion the patient was anergic. Following lymphocyte transfer cutaneous reactivity to DNCB was restored. Skin reactivity to mumps and varidase antigens was specifically transferred. Whole lymphocyte transfer is a feasible method for restoring immune competence in the anergic cancer patient.

Adolescent↗
PubMed1975

Suggestive evidence for in vivo binding of specific antitumor antibodies of human melanomas.

Antibodies eluted from homogenates of human melanoma cells reacted against melanoma cells reacted against melanoma antigens in a complement fixation test. Before elution, sonically treated homogenate did not react significantly against autologous serum but, following elution, antigenic activity increased markedly (up to 32-fold). Eluate of one melanoma reacted with the sonically treated residue of other melanomas but not with similarly prepared residues of sarcoma, carcinomas, or normal tissues. Melanoma eluates comtained more IgG than IgA. Traces of IgM were found in two melanoma eluates. Eluates of normal tissues (lung, kidney, and muscle) were devoid of serum proteins and did not react with the soncially treated melanoma residues. These results support the hypothesis that antitumor antibodies are bound to melanoma cells in vivo and that these antigens are cross-reactive.

Antibodies, Neoplasm↗
PubMed1975

Rheumatoid lung.

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Adult↗
PubMed1975

Studies on the extent of gill surface in a fresh water cat-fish Bagarius bagarius (Ham.).

The total gill area of the fish ranges from 37,537 to 56,551 lamellae. The number of lamellae per mm of the gill filament and area of lamellae knowing the respiratory gill area, the gill area per g of body weight and per cm3 of body volume were calculated to correlate the variation in gill surface area per unit weight and volume of the fish. The fish can survive for quite long out of water as the lamallae are spaced wide apart and do not adhere together.

Animals↗