Nucleotide sequence of psbQ gene for 16-kDa protein of oxygen-evolving complex from Arabidopsis thaliana and regulation of its expression.

The psbQ gene encoding a 16-kDa polypeptide of the oxygen-evolving complex of photosystem II has been isolated from Arabidopsis thaliana and characterized. The gene consists of a 28 nucleotide long leader sequence, two introns and three exons encoding a 223-amino-acid precursor polypeptide. The first 75 amino acids act as a transit peptide for the translocation of the polypeptide into the thylakoid lumen. Expression studies show that the gene is light-inducible and expresses only in green tissues with high steady-state mRNA levels in leaves. Using this gene as a probe, restriction fragment length polymorphism between two ecotypes, Columbia and Estland, has also been detected.     

Effects of 1-ethynylpyrene and related inhibitors of P450 isozymes upon benzo[a]pyrene metabolism by liver microsomes

The effects of three aryl acetylenes, 1-ethynylpyrene (EP), 2-ethynylnaphthalene (EN) and 3-ethynylperylene (EPE), upon the metabolism of benzo[a]pyrene (BaP) by microsomes isolated from rat liver were investigated. These aryl acetylenes all inhibited the total metabolism of BaP. Formation of BaP 7,8-dihydrodiol and BaP tetrol products by microsomal preparations from rats that had been pretreated with 3-methylcholanthrene (3MC) were preferentially inhibited. The effects of EP upon the metabolism of BaP 7,8-dihydrodiol by microsomes from rat liver were also studied. This aryl acetylene strongly inhibited the formation of BaP tetrols from BaP 7,8-dihydrodiol by liver microsomes both from untreated rats and from rats pretreated with 3MC, but enhanced the conversion of the BaP dihydrodiol into other metabolites.     

Metal Ion Interactions with Phosphoenolpyruvate Carboxylase from Crassula argentea and Zea mays

Metal ion interactions with phosphoenolpyruvate carboxylase from the CAM plant Crassula argentea and the C₄ plant Zea mays were kinetically analyzed. Fe²⁺ and Cd²⁺ were found to be active metal cofactors along with the previously known active metals Mg²⁺, Mn²⁺, and Co²⁺. In studies with the Crassula enzyme, Mg²⁺ yielded the highest V_max value but also generated the highest values of K_m(metal) and K_m(pep). For these five active metals lower K_m(metal) values tended to be associated with lower K_m(pep) values. PEP saturation curves showed more kinetic cooperativity than the corresponding metal saturation curves. The activating metal ions all have ionic radii in the range of 0.86 to 1.09 Å. Ca²⁺, Sr²⁺, Ba²⁺, and Ni²⁺ inhibited competitively with respect to Mg²⁺, whereas Be²⁺, Cu²⁺, Zn²⁺, and Pd²⁺ showed mixed-type inhibition. V_max trends with the five active metals were similar for the C. argentea and Z. mays enzymes except that Cd²⁺ was less effective with the maize enzyme. K_m(metal) values were 10- to 60-fold higher in the enzyme from Z. mays.     

Neurotrophin expression in rat hippocampal slices: a stimulus paradigm inducing LTP in CA1 evokes increases in BDNF and NT-3 mRNAs.

We report that stimulation inducing long-term potentiation (LTP) in the CA1 pyramidal cell layer of the hippocampus evokes significant increases in both BDNF and NT-3 mRNAs in CA1 neurons. No changes in BDNF or NT-3 mRNA levels were seen in the nonstimulated regions of the pyramidal cell layer or the dentate. No change was seen in the levels of NGF mRNA at the time point examined. These results suggest that relatively normal levels of activity may regulate region-specific neurotrophin levels in the hippocampus. Given that known effects of NGF (and presumably of BDNF and NT-3) include elevation of neurotransmitter levels, elevation of sodium channels, and promotion of axonal terminal sprouting, activity-associated changes in neurotrophin levels may play a role in regulating neural connections in the adult as well as the developing nervous system.     

Senescence of attached leaves: Regulation by developing pods

Analysis of total nitrogen, chlorophyll content, ribulose-1,5-bisphosphate carboxylase/oxygenase activity and net photosynthesis rate was carried out on the leaves that support the developing pods in pigeon pea [ Cajanus cajan (L.) Millsp. cv. Prabhat] at several stages during pod filling. A continuous loss in all the above-mentioned parameters was observed during the course of pod development. When no pods were allowed to develop by continuous flower removal treatment, there was a considerable delay in loss of all these metabolic parameters. Excision of pods after their mid-development resulted not only in no further loss, but also in a significant recovery both of total nitrogen and of other investigated characteristics.     

Ca-pumps in smooth muscle: one in plasma membrane and another in endoplasmic reticulum

For several years it has been debated whether the Ca-pump in smooth muscle is located in the plasma membrane or in the endoplasmic reticulum (alias sarcoplasmic reticulum). Experimental evidence using skinned smooth muscle cells and subcellular membrane fractions isolated from a number of smooth muscles is reviewed here to hopefully resolve this issue. The inescapable conclusion is that there are two modes of nonmitochondrial ATP-dependent Ca-transport. The first one, unaffected by oxalate, is localized in the plasma membranes and the second, potentiated by oxalate, is localized in the endoplasmic reticulum. Clear experiments to delineate the roles of the two pumps in the excitation-contraction cycle of the smooth muscle remain to be conducted.     

Hydrogen peroxide formation and lipid peroxidation in rat uterus—effect of hormones and vitamin E

The effect of estradiol-17β and progesterone given separately as well as in combination on the rate of hydrogen peroxide formation and lipid peroxidation in the uteri of ovariectomized rats was studied. Estradiol in 3μg dose per day per animal elicited maximum stimulatory response and progesterone (100μg), on the other hand, was without any such effect. However, progesterone given along with estradiol completely prevented the effect due to the latter. In the same way, vitamin E, a well known antioxidant was found to be extremelv effective in protecting the uterus from the highly peroxidative action of estradiol-17β.     

Reactions of polycyclic hydrocarbon epoxides with RNA and polyribonucleotides

RNA, poly(G) and poly(A) were reacted with benz[a]anthracene 5,6-oxide or with 7,12-dimethylbenz[a]anthracene 5,6-oxide and hydrolysates of the alkylated polymers examined using a combination of Sephadex LH20 column chromatography and thin-layer chromatography on silica gel. The results show that two RNA products are formed in reactions with benz[a]anthracene 5,6-oxide, one resulting from reaction with guanine and the other from reaction with adenine. With 7,12-dimethylbenz[a]anthracene 5,6-oxide, six RNA products appeared to be formed, two resulting from reactions with guanine and three from alkylation of adenine; the other product has not been identified.