Magnetic resonance studies of the proximity and spatial arrangement of propionyl coenzyme A and pyruvate on a biotin-metalloenzyme, transcarboxylase

A spin-labeled ester of CoA, R-CoA (3-carboxy-2,2,5,5-tetramethyl-1-pyrolidinyl-1-oxy CoA thioester), has been shown by competition studies using electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) to bind specifically to the propionyl-CoA binding sites of transcarboxylase. Titrations indicate 0.7 +/- 0.2 binding site for R-CoA per enzyme-bound biotin with a dissociation constant of 0.33 +/- 0.12 mM. Propionyl-CoA binds to this site with a 1.3-fold lower disonable agreement with kinetically determined inhibitor constants of CoA and propionyl-CoA and propionyl-CoA (D. B. Northrop (1969), J. Biol. Chem. 244, 5808). The bit of this spin-label on 1/T1 of water protons. The formation of a ternary transcarboxylase-R-CoA-pyruvate complex is suggested by the failure of pyruvate to displace R-CoA from the tight site and is established by the paramagnetic effects of enzyme-bound R-CoA on the relaxation rates of the protons and 13C atoms of enzyme-bound pyruvate. From the paramagnetic effects of R-CoA on the relaxation rates of the methyl protons of pyruvate at 40.5 and 100 MHz, and on the 13C-enriched carbonyl and carboxyl carbon atoms of pyruvate at 25.1 MHz, a correlation time of 7 nsec and distances from the bound nitroxide radical to the methyl protons, the carbonyl, and carboxyl carbon atoms of bound pyruvate of 7.9 +/- 0.7, 10.3 +/- 0.8, and 12.1 +/- 0.9 A, respectively, are calculated. These distances establish the close proximity of the CoA ester and keto acid sites on transcarboxylase. Together with the previously determined distances from the enzyme-bound (Co(II) to the methyl protons and 2 carbon atoms of bound pyruvate and to 12 protons and 3 phosphorus atoms of bound propionyl-CoA, the present distances are used to derive a composite model of the bound substrates in the overall transcarboxylation reaction. In this model the distance from the methyl carbon of pyruvate and the methylene carbon of propionyl-CoA, between which the carboxyl transfer takes place is only approximately 7 A. Depending on the detailed mechanism of the carboxyl transfer, the distance through which the carboxybiotin must migrate is therefore between 0 and 7 A. Hence the major role of the 14-A arm of carboxybiotin is not to permit a large carboxyl migration but, rather to permit carboxybiotin to traverse the gap which occurs at the interface of three subunits and to insinuate itself between the CoA and keto acid sites.

Residues of DDT and its metabolites in human blood samples in Delhi, India

Blood samples from 182 people in Delhi, India, were examined for DDT residues. All except 8 contained DDT and its metabolites. The average total DDT concentration in the whole blood ranged from 0.177 to 0.683 mg/litre in males and from 0.166 to 0.329 mg/litre in females. The DDT metabolites detected were p,p'-DDE, p,p'-DDD, and o,p'-DDT. DDE accounted for most of the total DDT.

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.

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.

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...

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.

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.

Constitution and synthesis of naturally occurring isopentenylated kaempferol derivatives, noranhydroicaritin and isoanhydroicaritin and related flavonolsincluding Di-O-methylicaritin

Kaempferol (20) reacted with 2-methylbut-3-en-2-ol in the presence of boron trifluoride etherate to yield a mixture of the 6,8-di(3- methylbut-2-enyl) derivative (21), 3,5-dihydroxy-2-(4?-hydroxyphenyl)- 8,8-dimethyl-9,10-dihydro-4H,8H-benzo[1,2-b:3,4-b?]dipyran-4-one (19), and natural noranhydroicaritin(5). The orientation of the 3-methylbut- 2-enyl unit in the 8-position in the flavonol(5) has been unambiguously established by synthetic experiments. Complete acetylation of the flavonol (5) followed by reaction of the product (22) with one molar proportion of methyl iodide in the presence of dry potassium carbonate and acetone afforded 8-(3-methylbut-2-enyl)rhamnocitrin triacetate (23) which, on deacetylation, gave natural isoanhydroicaritin3 (4). 3- Methylbut-2-enylation of kaempferol 3,4?-dimethyl ether (7) was effected in two ways and the products [(8), (9) and (10)]were oxidatively cyclized with 2,3-dichloro-5,6-dicyano-p-benzoquinone to make available the corresponding monopyrano derivatives (26)-(29) to act as reference compounds for investigation of natural products. The 3-methoxyflavone (10) was also converted into di-O-methylicaritin (24) via the partial methyl ether (17a).