SEARCH · Search PubMed
Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Concerning the problems of learning and memory there is a distinction of a short term memory (STM) and a long term memory (LTM). It is supposed that the STM is an electrical phenomenon, whereas the LTM depends on material changes. The assumed materials are RNA, proteins, lipids, amines etc, and the primary carrier of the information is DNA. But there is a discrepancy: learning-specificity is based on environmental changes, but not the structure of DNA. For the investigation of this, we trained goldfish in a shock-free task to take food from coloured cups under the influence of inhibitors of the proteinbiosynthesis. There was no inhibition on memory-processes in our experiments.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
A new uridine analog, 4-hydroxy-1-(beta-D-ribonfuranosyl)-pyridazin-6-one (3-deaza-6-azaUrd), inhibited the growth of L1210 cells in culture, with a concentration to reduce growth rate to 50% of control of 7 X 10(-5) M. After treatment for 24 or 48 h with 5 X 10(-4) M 3-deaza-6-azaUrd, 80% of the cells were unable to resume growth when the analog was removed from the cultures; also, 99% of the cells were killed, as determined by colony formation in soft agar. Studies on the prevention of the cytotoxic effects of 5 X 10(-4) M 3-deaza-6-azaUrd showed that uridine or cytidine gave complete protection. 2'-Deoxycytidine also gave partial protection, but orotic acid or thymidine had no effect on the growth inhibition by 3-deaza-6-azaUrd. These results suggested that growth inhibition by 3-deaza-6-azaUrd might be due to interference in pyrimidine biosynthesis. Activation of 3-deaza-6-azaUrd to its 5'-phosphate derivative appeared to be catalyzed by uridine kinase. 3-Deaza-6-azaUrd was shown to complete with uridine for phosphorylation (Ki = 4.7 mM) and, therefore, to be a possible alternative substrate for uridine kinase from mouse kidney (Km for uridine = 82 microM). The enzyme was partially purified by streptomycin sulfate precipitation, ammonium sulfate fractionation, and gel filtration. This preparation was found to be free of pyrimidine nucleoside phosphorylase and uridine monophosphate kinase.
Chemotherapy remains the major treatment modality in childhood acute nonlymphocytic leukemia (ANLL). Current remission induction rates range from 60% to 80%; but even with the improved rate of response to therapy, the median duration of remission has seldom exceeded 1 year. On the other hand, an increasing number of children with ANLL who were treated with intensive induction and maintenance chemotherapy regimens for a prescribed period followed by discontinuation of therapy are remaining in remission. The evolution of present-day chemotherapy approaches to childhood ANLL are reviewed in this article.
Explore the source record for details and available documents.
Pyrimidine synthesis and its regulation are presented. Among the disorders of human pyrimidine metabolism, hereditary orotic aciduria and that produced by drugs play the principal role. A rise in renal excretion of orotic acis is also observed when ornithine transcarbamylase activity is lacking. The importance of "orotic aciduria with partial response to folic acid" in pyrimidine metabolism is still not clear. Close relationship between the formation of pyrimidine and purine nucleotides must be assumed, because both enter into the synthesis of nucleic acid, for the greatest part in approximately equimolecular amounts. Possibly 5-phosphoribosyl-1-pyrophosphate plays an important part.
Explore the source record for details and available documents.
Partially purified calf brain uridine kinase precipitated by bivalent metal cations has been compared with the soluble enzyme fraction regarding its stability in the presence of inactivating factors. The freeze-dried preparations of uridine kinase precipitaated by Pb2+ or Zn2+ ions, althouth enzymatically highly active, are insoluble in aqueous solutions. The activity of metal-insolubilized enzymes disappears during their preincubation in acidic media or in the presence of silver ions. Also trypsin, chymotrypsin and cathepsin B1 caused decreases in enzyme activity. However, fractions which have been precipitated by metal ions and freeze-dried are stable at high temperatures, whereas the activity of soluble uridine kinase is completely lost. Both unheated metal-ion precipitated uridine kinase preparations and those heated at 100 degrees C are equally sensitive to the feedback inhibition by CTP.