DIFFERENCES IN THE REGULATION OF TYROSINE AMINOTRANSFERASE IN BRAIN AND LIVER

Abstract— l -Tyrosine:2-oxoglutarate aminotransferase (EC 2.6.1.5) activity in rat brain is not regulated in the same way as in rat liver. No diurnal rhythm in the activity of the cerebral enzyme was found in rats fed ad lib. although there was a marked diurnal variation in the activity of the hepatic enzyme. In adrenalectomized rats, hydrocortisone and glucagon induced the enzyme in liver but had no effect on the enzyme in brain. In normal rats, treatment with reserpine or exposure to cold elevated the activity of the hepatic enzyme without affecting the enzyme in brain. Thus, the tyrosine aminotransferase of brain differed from the enzyme in liver since it did not exhibit diurnal variations of activity and was not affected by hormones, drugs, or stress.     

Role of superoxide in radiation-killing of Escherichia coli and in thymine release from thymidine

The role of superoxide and hydroxyl radicals in gamma-radiation-killing of Escherichia coli K12 was studied in aerated suspensions supplemented with formate, phosphate, superoxide dismutase, catalase and saturated with nitrous oxide. Nitrous oxide, which converts e-aq to .OH, caused decreased radiosensitivity. On the other hand, formate, which results in conversion of .OH to .O2-, resulted in an increased radiosensitivity. The results implicated .O2- as a major cause of radiation-mediated cell-killing. The addition of the enzymes, superoxide dismutase or catalase to the E. coli suspensions prior to and during irradiation had no effect on cell survival, indicating that the biologically significant site of generation and action of .O2- is an intracellular one. Further studies were undertaken to examine the role of superoxide in DNA damage. The release of thymine from the DNA base, thymidine was studied as a result of gamma-irradiation and of chemically generated superoxide (using KO2 in dimethyl sulfoxide). Thymine was identified by HPLC and mass spectrometry. C-13 NMR analysis of the reaction mixture of thymidine with KO2 in dimethyl sulfoxide provided evidence for attack of .O2 at the ribosyl Cl' atom.     

Effects of the thyroid status on the sarcoplasmic reticulum in slow skeletal muscle of the rat

The effects of the thyroid status on the Ca++-transporting capabilities of rat slow skeletal muscle (m.soleus) were studied. The oxalate supported Ca++-uptake activity and Ca++-loading capacity of muscle homogenates from hyperthyroid rats showed an approximate 4.2 and 2.5 fold increase, respectively, as compared to values found in the hypothyroid group. Muscle homogenates of euthyroid rats gave intermediate values. The specific activity of oxalate supported Ca++ uptake, but not the Ca++-loading capacity, of membrane preparations enriched with respect to sarcoplasmic reticulum (SR) increased in proportion to the thyroid status. This was paralleled by a 3.5 fold increase in the amount of active Ca++ pumps in the SR preparations in the transition from hypothyroidism to hyperthyroidism as determined by measurement of Ca++-dependent 32P incorporation. These observations are not explained by differences in degree of purification of the examined SR preparations. Protein profiles of the membrane preparations obtained by gel electrophoresis indicated a thyroid-hormone dependent increase in Ca++-pump content relative to other SR proteins. The results suggest that thyroid hormone stimulates the proliferation of the SR and possibly also increases the Ca++-pump density in the SR membrane.     

Germination,reproduction and interference in the amphicarpic annual Emex spinosa (L.) Campd

Summary A comparison was made of the dimorphic subterranean and aerial achenes of the annual Emex spinosa (L.) Campd. Subterranean achenes were less dormant, had a higher percentage of viability, germinated at a faster rate, were less temperature-dependent in germination and produced larger seedlings than aerial achenes. Subterranean achenes germinated, equally well in light or dark but aerial achenes had a strong light requirement. There was a linear relationship between numbers of weight of aerial achenes and plant size in the field. More resources were allocated to reproduction in plants restricted in size because of environmental conditions. Subterranean achene production was less affected than aerial by density, nitrogen levels, varying field conditions and interference between plants grown, from subterranean and aerial achenes. In mixtures of such plants, those from subterranean achenes had larger leaf area and stems and more aerial achenes. These differences were not apparent in monocultures by the time of harvest. Seed dimorphism is more likely in short-lived fugitive species and the different roles associated with dimorphism (persistence in situ versus dispersal in E. spinosa) are seen as an ecological advantage in such species.