Aggregation of human lymphoblastoid cells by tumor-promoting phorbol esters and dihydroteleocidin B

Human lymphoblastoid cells transformed by Epstein-Barr virus aggregated rapidly in the presence of tumor-promoting phorbol esters and dihydroteleocidin B. Cell aggregation was almost complete after incubation for 6 hours. In amounts of a few ng, they induced significant aggregation. Their abilities to aggregate cells could be measured quantitatively and correlated well with their effects in promoting skin tumors.     

Hydroxyurea inhibits ODC induction, but not the G1 to S phase transition.

Chinese hamster ovary cells, selected in mitosis and plated into medium containing hydroxyurea, can progress through G₁ and enter S phase although bulk DNA synthesis is prevented. As the cells progress through G₁ in the presence of hydroxyurea, ornithine decarboxylase activity remains low while general protein synthesis appears unaffected. After hydroxyurea is removed, ornithine decarboxylase activity increases, but only after approximately 20% of the DNA has been replicated. These results suggest that ornithine decarboxylase induction is not essential for cellular progression into S phase but is required for the completion of DNA synthesis.     

Early hCG-induced desensitization in Leydig cells.

The early mechanism of hCG induced down regulation of its own receptor as well as steroidogenesis refractoriness of rat Leydig cells to gonadotropin stimulation have been investigated. A single injection of 5, 12, 25, 50 and 100 IU of hCG in rats induced within 8 hours, Leydig cells desensitization. However, apparent receptor loss was significantly lower only in the rats who received 50 and 100 IU of hCG. Cycloheximide inhibits hCG-induced receptors loss but had no effect on hCG-induced desensitization. The most likely explanation for desensitization in the presence of binding sites and a normal adenylate cyclase, is a defective coupling between the receptor sites and the catalytic subunit.     

Regional and subcellular distribution of cysteine sulfinate transaminase in rat nervous system

The distribution of the cysteine sulfinate transaminase activity in adult and newborn rat central nervous system was studied and compared with the distribution of the glutamate oxaloacetate transaminase activity. The subcellular localization of both enzyme activities was also investigated. These experiments suggest that both enzymes, sometimes considered as identical, are different.     

ATP synthesis in a succinate decarboxylase system from Fasciola hepatica mitochondria

Köhler P. B.,Ryant C. and Behm Carolyn A. 1978. ATP synthesis in a succinate decarboxylase system from Fasciola hepatica mitochondria. International Journal for Parasitology8: 399–404. Succinate decarboxylation was measured by the formation of ¹⁴CO₂ from 1,4-¹⁴C-succinate in a particle free, dialysed mitochondrial extract from liver fluke. It has an absolute requirement for Mg²⁺ and CoA. ATP, ADP and inorganic phosphate are essential for optimal activity. Ap₅A, an inhibitor of adenylate kinase, and glutathione are also necessary. GTP supports decarboxylation as well as ATP, provided ADP is also present. The formation of CO₂ and propionate greatly exceeds the amount of ATP and CoA initially present in the reaction mixture. A net, substrate-level phosphorylation of ADP occurs, the amount of ATP formed being equivalent to the production of CO₂ or propionate. This system is inhibited in flukes incubated in vitro with mebendazole.It is concluded that ATP is required to spark the fermentation system when succinate is the initial substrate and intermediate substrates are absent; that the terminal step in propionate formation is catalysed by a transferase which transfers CoA from propionyl CoA to succinate; and that ATP formation is coupled to the decarboxylation of methylmalonyl-CoA. A reaction scheme is presented.     

Terminal deoxyribonucleotidyl transferase activity in acute undifferentiated leukemia.

Guanosine, rather than its methylated derivative, was found to be the inverted nucleoside present in the 5′ terminal capping structure of insect oocyte messenger RNA. Since methylation of the terminal guanosine at the 7 position is necessary for the initiation of protein synthesis in eukaryotes, this evidence suggests that the translational inactivity of the mRNA prior to fertilization may be associated with the absence of methylation.