Absolute configuration of the 5,6-oxide formed from 7,12-dimethylbenz[a]anthracene by cytochrome P450c

The absolute configurations of the enantiomeric 5,6-arene oxides of 7,12-dimethylbenz[a]anthracene (DMBA) were recently assigned such that the late eluting enantiomer from a chiral HPLC column has 5R,6S absolute configuration. [Mushtaq et al. (1984) BBRC 125, 539]. The authors further concluded that the 5R,6S-enantiomer predominates on metabolism of DMBA by cytochrome P450c in liver microsomes from 3-methylcholanthrene-treated rats. Their chemical assignment of absolute configuration is incorrect. Thus, metabolism of DMBA by these microsomes as well as by homogeneous cytochrome P450c produces 5,6-oxide highly enriched (95%) in the 5S,6R-enantiomer in accord with theoretical predictions.     

Effect of Lincocin Treatment on the Greening Process in Bean (Phaseolus vulgaris) Leaves

The effect of lincocin (a plastid protein synthesis inhibitor) treatment on the greening process of bean (Phaseolus vulgaris L.) leaves have been studied. In comparison with control leaves treated ones had a decreased rate of chloroplast development. They had a marked chlorophyll deficiency and a decreased chlorophyll a/b ratio. Some long and short wavelength forms of chlorophyll a were lacking as evidenced from the absorption spectra at 25°C and the fluorescence spectra at 77°K. The –¹⁴CO₂ fixation was inhibited by 80–90% in treated leaves. The fluorescence induced by the measuring light was greater in the treated leaves than in the control ones, and the kinetics of the decline of the relative fluorescence intensity were also different. Electron microscopic studies showed macrogranum-like structures and incomplete membrane vesicles in the treated plastids. After longer treatment a destruction of membranes was observed. The results indicate some structural and functional membrane deficiencies and instability of the membranes.     

Lecithotrophic development and metamorphosis in the Indo-West Pacific brittle star Ophiomastix venosa (Echinodermata: Ophiuroidea)

Summary

The larval development of the ophiocomid ophiuroid Ophiomastix venosais described using SEM. The gastrula transforms into a uniformly ciliated early larva which progressively changes into a lecithotrophic late premetamorphic larva with a continuous bilateral ciliated band. This stage is short-lived and equivalent to a highly reduced ophiopluteus. Comparisons between O. venosa and other ophiuroid species whose development has been investigated suggest that, whatever the developmental mode (lecithotrophic or planktotrophic), a pluteus stage always occurs in ophiuroids with planktonic development. Two metamorphic stages were identified, the late metamorphic larva differing from the early one by the closure of the larval mouth. The appearance of the permanent mouth marks the end of the metamorphosis. The postlarva still possesses remnants of larval features. The transformation of the reduced ophiopluteus into a barrel-shaped metamorphic larva with transverse ciliated bands, a vitellaria larva, is followed. The possible occurrence of a unique type of metamorphic larva in non-brooding ophiuroids is discussed. Verification of this, however, needs further SEM investigations on metamorphic larva from species having “regular” planktotrophic development.     

Individual subunits of the glutamate transporter EAAC1 homotrimer function independently of each other

Glutamate transporters are thought to be assembled as trimers of identical subunits that line a central hole, possibly the permeation pathway for anions. Here, we have tested the effect of multimerization on the transporter function. To do so, we coexpressed EAAC1(WT) with the mutant transporter EAAC1(R446Q), which transports glutamine but not glutamate. Application of 50 microM glutamate or 50 microM glutamine to cells coexpressing similar numbers of both transporters resulted in anion currents of 165 and 130 pA, respectively. Application of both substrates at the same time generated an anion current of 297 pA, demonstrating that the currents catalyzed by the wild-type and mutant transporter subunits are purely additive. This result is unexpected for anion permeation through a central pore but could be explained by anion permeation through independently functioning subunits. To further test the subunit independence, we coexpressed EAAC1(WT) and EAAC1(H295K), a transporter with a 90-fold reduced glutamate affinity as compared to EAAC1(WT), and determined the glutamate concentration dependence of currents of the mixed transporter population. The data were consistent with two independent populations of transporters with apparent glutamate affinities similar to those of EAAC1(H295K) and EAAC1(WT), respectively. Finally, we coexpressed EAAC1(WT) with the pH-independent mutant transporter EAAC1(E373Q), showing two independent populations of transporters, one being pH-dependent and the other being pH-independent. In conclusion, we propose that EAAC1 assembles as trimers of identical subunits but that the individual subunits in the trimer function independently of each other.     

Identification and structure-activity relationships of a new series of Melanocortin-4 receptor antagonists

The identification and optimization of a series of acylguanidine-based melanocortin-4 receptor antagonists is discussed.     

Stereoselective formation of benzo(c)phenanthrene (+)-(3S,4R) and (+)-(5S,6R)-oxides by cytochrome P450c in a highly purified and reconstituted system

The principal oxidative metabolites formed from benzo(c)phenanthrene (B(c)Ph) by the cytochromes P450 in liver microsomes from control and treated rats are the 3,4- and 5,6-arene oxides. A procedure is described which allows determination of the enantiomer composition and absolute configuration of these arene oxides based on HPLC separation of isomeric thiolate adducts formed with N-acetyl-L-cysteine in base. Incubation of [3H]-B(c)Ph with highly purified cytochrome P450c in a reconstituted monooxygenase system followed by trapping of the metabolically formed arene oxides as above indicated that the 3,4-oxide was predominantly the (+)-(3S,4R)-enantiomer (90%) and that the 5,6-oxide consisted mainly of the (+)-(5S,6R)-enantiomer (76%). The results are discussed in terms of their implications about the catalytic binding site of cytochrome P450c.