Sites of action of fusidic acid in eukaryotes. Inhibition by fusidic acid of a ribosome-independent GTPase from Artemia salina embryos.

1. A ribosome-independent GTPase activity has been isolated from the high-speed supernatant fraction of Artemia salina embryos, and some of its properties have been studied. This activity is inhibited by fusidic acid, an antibiotic generally thought to inhibit only EF-2 in eukaryotes. However, several lines of evidence indicate that the GTPase activity, described here, is distinct from EF-2. The results suggest, therefore, that the inhibitory effect of fusidic acid in eukaryotic systems is not restricted to EF-2 (and ribosome)-dependent functions only. 2. The results of other experiments have revealed that, despite its ability to inhibit the GTPase activity mentioned above, fusidic acid is not a non-specific inhibitor of all ribosome-independent GTPase and ATPase activities present in eukaryotic cells.     

STUDIES ON THE REGULATION OF GABA SYNTHESIS: SUBSTRATE-PROMOTED DISSOCIATION OF PYRIDOXAL-5''-PHOSPHATE FROM GAD

The association between glutamate decarboxylase (GAD) and its cofactor, pyridoxal-5′-phos-phate (pyridoxal-P), was studied using 20,0000 supernatant of rat brain. In this preparation GAD required added pyridoxal-P to maintain a linear reaction rate beyond 5 min of incubation. Following exhaustive dialysis the enzyme was more than 83% saturated with cofactor indicating that the cofactor was tightly bound to the enzyme. When incubations were performed in the presence of glutamate and without added pyridoxal-P there was a progressive inactivation of the enzyme which was dependent on the glutamate concentration. This lost activity was almost completely recovered by addition of pyridoxal-P to the dialyzed glutamate-inactivated enzyme. The results suggest that glutamate inactivates GAD by promoting the dissociation of pyridoxal-P from the enzyme thereby producing inactive apoen-zyme which can be reactivated by combining with available pyridoxal-P. This interpretation is supported by the finding that progress curves for the reaction were accurately described over a 30 min incubation period and 10-fold glutamate concentration range by an integrated rate equation which takes the glutamate-promoted dissociation of cofactor into account. The progressive inactivation could not be attributed to denaturation of the enzyme, impurities in the substrate, effects of pH, depletion of substrate, protein concentration, sulfhydryl reagents or product inhibition. The results presented here also show that certain precautions must be adopted to accurately measure GAD activity in the absence of added pyridoxal-P as has been widely done in studies of drug action. Specifically, measurements must be made at short times of incubation and low concentrations of glutamate to minimize the glutamate-promoted inactivation of the enzyme.     

Naturally occurring flavans unsubstituted in the heterocyclic ring

The naturally occurring free and glycosylated flavans are reviewed. The distribution, methods of isolation and structure elucidation of flavans, by comprehensive spectral analyses, are presented. Biological properties of flavans are appraised.     

Molecular mechanics aided design of antineoplastic agents from ruthenium coordinate complexes.

Through energy minimization using molecular mechanics force field four ruthenium cordinate complexes have been synthesized. Compound I to IV showed antineoplastic activity with varying degree on EAC bearing mice. Mode of action may be through inhibition of antioxidant property of tumor cell as evident from lipid peroxidase activity. Among the complexes Bis pyridine tetrachloro ruthenium exhibits highest order of activity with respect to increase mean survival time, inhibition of tumour volume, total blood count, hemoglobin and lipid peroxidase activity.     

New tetraoxygenated xanthones of Canscora decussata

From the alcoholic extract of Canscora decussata Schult (Gentianaceae), the previously unreported 1,3,6,7-tetrahydroxyxanthone (I), 1,3,5,6-tetrahydroxyxanthone-C₂-glucoside (II), and 1,5,6-trihydroxy-3-methoxyxanthone (III), have been isolated and identified. The structures of these xanthones have been established by chemical transformations, synthesis (in case of III), and spectral (UV, IR, PMR, MS) evidence. II and III have not been encountered before in nature, while I is reported for the first time in this genus. The significance of mass spectral fragmentation in the structural elucidation of oxygenated xanthones is discussed.     

Effect of chlorpromazine and gossypol on Ca(2+)-ATPase activity in the microsomal membranes of rat testes.

The microsomal membranes isolated from rat testes have been found to contain a Mg(2+)-dependent and a Mg(2+)-independent Ca(2+)-ATPase. The enzyme activities were inhibited by two contraceptive drugs--gossypol and chlorpromazine. The inhibition by the former was affected by the presence of ligand(s) and not the substrate in the incubation medium, whereas ligand(s)/substrate did not affect the inhibition by chlorpromazine. This may be explained from the fact that the binding of chlorpromazine and ligand(s)/substrate to the enzyme are independent of each other whereas in case of gossypol the ligand(s) compete with the drug at the binding site of the enzyme.     

Determination of amylase activity in bovine serum and its association with the Ami and Amll loci

Amylase activity has been estimated in the sera of 213 cattle by an amyloclastic method with potato amylose as the substrate with the addition of CaCl₂. The method has been developed from that of Street and Close to overcome the problems of the high colour of bovine serum which would otherwise interfere with the assay. A relationship has been found between the serum amylase genotype detected on starch-gel and the total enzyme activity. The enzymes AmI-B and AmII-B in homozygous combinations have been found to have the highest activities. Age of animal has no significant effect on the total enzyme activity. Activity has been investigated in sera from three separate cattle populations and it has been found to be a highly heritable character. Heritability estimates of 49 % and 39 % by sib analysis and 75 % by the twin method have been obtained.