A transfer nuclear Overhauser effect study of coenzyme binding to distinct sites in binary and ternary complexes in glutamate dehydrogenase

The oxidized coenzyme NAD binds to two sites per subunit of bovine liver glutamate dehydrogenase with equal affinity in the absence of dicarboxylic acid coligands. In the presence of glutarate or 2-oxoglutarate, the affinity to one site is unchanged, but the affinity to the other (presumed to be the active site) is considerably increased and now requires two dissociation constants to describe its saturation. A combination of transfer nuclear Overhauser effects (TRNOE) together with an examination of the slopes of TRNOE time dependence indicates that while NAD is bound in a syn conformation at both binding sites, NADP (which binds only to the active site) is bound in a syn-anti mixture. The existence of N6 to N3' and N6 and N2' and N1' to N3' NOE's with NAD suggests that the two coenzyme binding sites are located near enough to allow intermolecular NOE's. In the presence of 2-oxoglutarate where only binding to the active site is effectively observed, the conformation of either coenzyme is syn. Modeling studies using the distance estimates from the TRNOE results suggest that the nicotinamide ribose approximates a 3'-endo conformation. The absence of evidence for intermolecular NOE's under these conditions indicates that while the active and regulatory NAD sites per subunit are in close proximity, the six active sites per hexamer are located greater than 5 A apart.

Synthesis and antitumor activity of tropolone derivatives. 6. Structure-activity relationships of antitumor-active tropolone and 8-hydroxyquinoline derivatives

The bis derivative 6 of 8-hydroxyquinoline, which, like tropolones, readily forms a chelate, was synthesized and found to have high potency (dose = 12.5 mg/kg, T/C % = 164) against leukemia P388 in mice approximately equivalent to that of the bistropolone 1b. 8-Hydroxyquinoline analogues with broad structural variation were synthesized and their structure-activity relationships followed the same pattern as in the tropolone series. In addition, the bistropolones 1a-e were tested for their ability to bind to tubulin and found to have no such property. The results of this study suggested that bistropolone and bis(8-hydroxyquinoline) derivatives must form a chelate with the metal necessary for the enzyme, such as ribonucleotide reductase, which catalyzes the DNA biosynthetic pathways.

Antiprotozoal activity of diospyrin towards Leishmania donovani promastigotes in vitro

Diospyrin, a bis-naphthoquinone derivative, isolated from a plant, known for its antitumour properties against Ehrlich ascites carcinoma in Swiss A mice, exhibits antiprotozoal activity towards L. donovani promastigotes in culture.

Complete or partial homozygosity of chromosome 13 in primary retinoblastoma

Sixteen retinoblastomas were examined with chromosome 13 polymorphic probes to determine the frequency of homozygosity for the chromosome in the tumors. Each of the tumors had two cytogenetically normal appearing No. 13 chromosomes. Nontumorous cells from the same patients were heterozygous for the various polymorphic chromosome 13 probes used. At least partial homozygosity for a single chromosome 13 was observed in 75% of the tumors. These studies confirm and extend previous studies which suggest that homozygosity or hemizygosity at RBI occurs in the majority of retinoblastomas. We also demonstrate in an additional tumor that rapid clonal evolution from hemizygosity to homozygosity can occur in the tumor.

Kinetics of association and dissociation of colchicine-tubulin complex from brain and renal tubulin. Evidence for the existence of multiple isotypes of tubulin in brain with differential affinity to colchicine

The kinetics of colchicine binding to bovine brain tubulin have been reported to be biphasic under pseudo first order conditions [(1978) Biochemistry 17, 4466-4472]. Unlike brain tubulin, the kinetics of colchicine binding to bovine renal tubulin are monophasic. The apparent on-rate constant for the binding of colchicine to renal tubulin is found to be very close to that of the faster binding component in brain tubulin. Similarly, the dissociation of colchicine-tubulin complex in the presence of iodide is biphasic for brain tubulin but monophasic for renal tubulin. Since brain and renal tubulin apparently differ in beta-tubulin, our results suggest that the biphasic nature of the kinetics for bovine brain tubulin could possibly originate from the existence of multiple isotypes of tubulin differing in drug binding affinity.

Mast cells and idiopathic male infertility

Eighty-three testicular biopsies, done for evaluation of oligozoospermia and azoospermia, were reviewed. Biopsies from eight healthy fertile males served as control. Johnsen's scoring was used for the staging of spermatogenesis. The number of mast cells was counted in a 1-mm2 area to study the relationship of spermatogenesis and mast cell proliferation. An impairment of spermatogenesis was noticed as the mast cell density increased. When the Johnsen score ranged between 1 and 4, mast cells were 24 to 112, with a mean of 57.7 cells/mm2. This value was highly significant when compared with control cases (P less than .001).

Extended use of the Mustardé dancing man procedure

Webs other than epicanthal folds can be corrected by the Mustardé "dancing man" procedure. A series of 20 patients is presented in whom this method has been used to correct either minor degrees of congenital syndactyly or burn scar contractures in fingers.

The role of the B-ring of colchicine in the stability of the colchicine-tubulin complex

The binding of colchicine to tubulin is a slow, temperature-dependent and a poorly reversible process. Colchicine analogues modified in the B-ring of colchicine have been reported to bind to tubulin fairly rapidly (Ray, K., Bhattacharyya, B. and Biswas, B.B. (1981) J. Biol. Chem. 256, 6241-6244). In an effort to test the role of the B-ring in the reversibility of the colchicine-tubulin binding reaction, we have studied the kinetics of dissociation of the drug-tubulin complex for two B-ring-modified colchicine analogues under conditions in which the association reaction was blocked with a 40-fold excess of podophyllotoxin. In both cases, the dissociation was biphasic. The off-rate constants were determined and the results strongly suggest that the B-ring part of colchicine is responsible for the stability of the drug-tubulin complex. The dissociation data have been explained in terms of a binding model in which the binding of colchicine to tubulin involves a three-subdomain interaction rather than the previously suggested two-subdomain model (Andreu, J.M. and Timasheff, S.N. (1982) Biochemistry 21, 534-543).

The interaction of cystamine with bovine brain tubulin

Microtubule assembly in vitro is sensitive to a variety of non-physiological sulfhydryl-oxidizing agents, but the physiological significance of this phenomenon is unknown, since no physiological sulfhydryl-oxidizing agent has been shown to affect microtubule assembly in vitro. We have accordingly investigated the interaction of tubulin with cystamine. We have found that millimolar concentrations of cystamine inhibit microtubule assembly and induce an abnormal form of tubulin polymerization. Cystamine-induced polymerization does not occur at cold temperature. Formation of the polymer requires reaction of cystamine with two sulfhydryls which become available at 37 degrees C. In addition, cystamine reacts with about three sulfhydryls at 0 degrees C without inducing polymerization. This latter set of sulfhydryls appear to include one or both of the previously defined beta s sulfhydryls whose reaction with N, N'-ethylene-bis(iodoacetamide) is markedly inhibited by GTP, maytansine and vinblastine [Roach, M. C. & Luduena, R. F. (1984) J. Biol. Chem. 259, 12063-12071]. Cystamine's specific manner of interacting with tubulin suggests that it may mimic an endogenous sulfhydryl-directed regulator of microtubule assembly.

Digital reconstruction using the distally based osteofasciocutaneous radial forearm flap

The Chinese forearm flap is a versatile flap in hand reconstruction. Five cases are reported. The mechanism and reliability of retrograde venous return is discussed.

Digital Volar Amelanotic Malignant Melanoma in a Child

Malignant melanoma in childhood is rare. An unusual case of amelanotic melanoma of the volar thumb in a fourteen-year-old boy which posed problems of recognition and management is presented.

Digital volar amelanotic malignant melanoma in a child

Malignant melanoma in childhood is rare. An unusual case of amelanotic melanoma of the volar thumb in a fourteen-year-old boy which posed problems of recognition and management is presented.