Epilepsy and Oral Contraception

A controlled cross-over trial in 20 epileptic women, receiving regular anticonvulsant therapy showed that an oral contraceptive with a low oestrogen/ progestogen content had no significant effect on the average frequency of fits compared with identical dummy tablets.     

Bacteriochlorophyll and Heme Synthesis in Rhodopseudomonas spheroides: Possible Role of Heme in Regulation of the Branched Biosynthetic Pathway

Synthesis of heme, measured by incorporation of iron-59, and of bacteriochlorophyll was studied with wild-type and mutant strains of Rhodopseudomonas spheroides. The wild type formed heme from glycine and succinate at one-fortieth the rate of bacteriochlorophyll under anaerobic-light conditions. Added delta-aminolevulinate stimulated heme synthesis 10-fold without increasing bacteriochlorophyll production. Heme synthesis from glycine and succinate was increased when the magnesium branch of the biosynthetic path was curtailed by mutation or by p-fluorophenylalanine or 8-azaguanine. Synthesis of bacteriochlorophyll by the wild type from glycine and succinate stopped immediately after addition of puromycin, but heme production continued for a period. Porphyrins and other precursors did not appear upon addition of puromycin alone, but simultaneous addition of o-phenanthroline resulted in the accumulation of coproporphyrin. Production of this porphyrin by a mutant strain with impaired ability to form heme was unaffected by puromycin. Heme synthesis from glycine and succinate or from delta-aminolevulinate was decreased by limitation of methionine; it is suggested that coproporphyrin accumulation from glycine and succinate under conditions of methionine deficiency results from relief of feedback inhibition of delta-aminolevulinate synthase by heme. The development of delta-aminolevulinate synthase activity in response to low aeration is prevented by addition of delta-aminolevulinate. This repressive action of the latter is abolished when its conversion to heme is impeded by mutation or by methionine deficiency. It is suggested that heme, the quantitatively minor end product of the branched biosynthetic pathway, may regulate the flow of common intermediates when utilization of protoporphyrin by the magnesium branch is diminished. This regulation may be exerted by feedback inhibition of delta-aminolevulinate synthase and also by repression of enzyme formation.     

Studies on ferrochelatase. The enzymic formation of haem in proplastids, chloroplasts and plant mitochondria

1. Ferrochelatase was demonstrated in the chloroplasts and proplastids isolated from the primary leaves of beans (a dicotyledon) and oats (a monocotyledon). It was also detected in chloroplasts from etiolated bean seedlings made green by illumination before being harvested. The specific activities of the three types of bean organelles are similar, as are the specific activities of the oat proplastids and chloroplasts. 2. Chloroplasts from young spinach leaves also contain ferrochelatase; these chloroplasts were tested for their ability to form magnesium tetrapyrroles and found unable to catalyse the insertion of Mg(2+) into mesoporphyrin IX. 3. Ferrochelatase was also detected in potato tuber mitochondria. 4. Ferrochelatase activity in these plant preparations is much less stable on storage than similar preparations from bacteria and animal tissues. 5. Temperature affects the activities of spinach chloroplast ferrochelatase and rat liver ferrochelatase differently. Activity of the chloroplast enzyme increases as the temperature rises from 20.6 degrees to 26 degrees , but becomes increasingly inactivated as the temperature rises further to 38 degrees . The initial velocity of the mammalian enzyme, however, increases as the temperature rises from 25.8 degrees to 65 degrees , but the enzyme is inactivated after several minutes at 65 degrees .     

Phosphorylation of choline and ethanolamine in Ehrlich ascites-carcinoma cells

1. Ehrlich ascites-cell extracts convert choline and ethanolamine approximately equally well into their respective phosphoryl derivatives. 2. Choline is a potent inhibitor of ethanolamine phosphorylation, but ethanolamine has little effect on choline phosphorylation. 3. 2,3-Dimercaptopropanol, cysteine and Ca(2+) inhibit ethanolamine phosphorylation, but have no detectable effect on choline phosphorylation. 4. Choline-phosphorylating activity in Ehrlich ascites-cell extracts is more stable during storage than ethanolamine-phosphorylating activity. 5. Choline phosphorylation is stimulated in the presence of benzoylcholine, succinylcholine, butyrylcholine and propionylcholine, whereas ethanolamine phosphorylation is inhibited. This relationship is reciprocal: the compounds causing the greatest stimulation of choline phosphorylation bring about the greatest inhibition of ethanolamine phosphorylation.     

Increases in tyrosine phosphorylation are detectable before phospholipase C activation after T cell receptor stimulation.

Antiphosphotyrosine immunoblots were used to characterize tyrosine phosphorylated proteins after stimulation of the human TCR. Increased tyrosine phosphorylation was evident on at least 12 substrates within 2 min after ligation of the TCR with mAb. Analysis of the time course for increased tyrosine phosphorylation revealed distinct patterns. Increased phosphorylation of 135-kDa and 100-kDa substrates was evident within 5 s, whereas increased phosphorylation of the TCR-zeta-chain required several minutes after treatment with anti-CD3 mAb. This rapid cellular tyrosine phosphorylation occurred independent of the cell cycle, as it occurred after stimulation of resting T cells, T cell blasts, and the Jurkat T cell leukemia line. When the TCR complex was cross-linked together with the CD4 receptor by heteroconjugate anti-CD3/CD4 mAb, an increased magnitude of tyrosine phosphorylation occurred, although no new substrates could be detected. The increased tyrosine phosphorylation of the 135-kDa and 100-kDa substrates was specific in that anti-HLA class I, anti-CD6, anti-CD7, and anti-CD28 antibodies did not cause increased tyrosine phosphorylation. Anti-CD4 stimulation of resting T cells did not cause increased tyrosine phosphorylation of pp100 and pp135, suggesting that the CD4-associated kinase, lck, does not account for the tyrosine phosphorylation observed after TCR stimulation. Similarly, pharmacologic treatment of cells with phorbol ester and calcium ionophore did not cause increased tyrosine phosphorylation of these substrates, indicating that activation of protein kinase C or phospholipase C does not account for these early increases in tyrosine phosphorylation. The time of onset of pp100 phosphorylation, and the magnitude of phosphorylation correlated with the magnitude of calcium mobilization when cells were stimulated with different forms of TCR stimulation. When cells were labeled with [3H]myoinositol and analyzed after stimulation by anti-CD3 mAb, increased tyrosine phosphorylation of the 135-kDa and 100-kDa substrates preceded the activation of phospholipase C, as measured by the appearance of inositol 1,4,5-trisphosphate. This occurred in both T cell blasts and in the Jurkat T cell line. Thus, these findings show that increased tyrosine phosphorylation is the earliest yet detected signal observed after ligation of the TCR complex, and furthermore suggest that tyrosine phosphorylation might link the TCR to the phosphatidylinositolbisphosphate hydrolysis signaling pathway.     

CD28 is an inducible T cell surface antigen that transduces a proliferative signal in CD3+ mature thymocytes

The rearrangement of TCR genes during thymic ontogeny creates a repertoire of T cell specificities that is refined to ensure the deletion of autoreactive clones and the MHC restriction of T cell responses. Signals delivered via the accessory molecules CD2, CD4, and CD8 have a crucial role in this phase of T cell differentiation. Recently, CD28 has been identified as a signal transducing molecule on the surface of most mature T cells. Perturbation of the CD28 molecule stimulates a novel pathway of T cell activation regulating the production of a variety of lymphokines including IL-2. We have studied the expression and function of CD28 during thymic ontogeny, and in resting and activated PBL. A variable percentage of resting thymocytes were CD28+ (3 to 25%, n = 8), but it was found in high density only on mature CD3+(bright) CD4/CD8 cells. Both unseparated thymocytes and isolated CD3-CD28-/dull cells proliferated when stimulated with PMA plus IL-2 or PMA plus ionomycin. PMA treatment also rapidly up-regulated CD28 expression in the CD3- subset as these cells became CD3-CD28+(bright). Despite the ability of PMA to induce high density CD28 expression in CD3- cells, CD3- thymocytes did not proliferate in response to PMA plus anti-CD28 mAb, in contrast to unseparated cells. CD3+ thymocytes stimulated with immobilized anti-CD3 mAb also failed to proliferate in culture. However, the addition of either IL-2 or anti-CD28 mAb supported proliferation, suggesting that only CD3+ cells could respond to CD28 signaling. The comitogenic effect of anti-CD3 and anti-CD28 mAb was IL-2 dependent as it was abrogated by an anti-IL-2R mAb. Interestingly, the expression of CD28 on the cell surface of CD3+ cells was also inducible, as flow cytometric analysis demonstrated a 10-fold increase in cell surface CD28 by 24 to 48 h after anti-CD3 stimulation of both CD3+ thymocytes and peripheral blood T cells. This increase was accounted for by a commensurate increase in CD28 mRNA levels. Together, these results suggest that CD28 is an inducible T cell antigen in both CD3- and CD3+ cells. In addition, stimulation of the CD28 pathway can provide a second signal to support the growth of CD3+ thymocytes stimulated through the TCR/CD3 complex, and may therefore represent a mechanism for positive selection during thymic ontogeny.