The regulation of exogenous NAD(P)H oxidation in spinach (Spinacia oleracea) leaf mitochondria by pH and cations.

Essentially chlorophyll-free mitochondria were isolated from green leaves of spinach (Spinacia oleracea L. cv. Viking II). Uncoupled oxidation of exogenous NADPH (1 mM) to oxygen had an optimum at pH 6.0, and activity was relatively low at pH 7.0, even in the presence of 1 mM-CaCl2. There was a proportional increase in the apparent Km for NADPH with decreasing H+ concentrations, suggesting that NADPH protonated on the 2'-phosphate group was the true substrate. Exogenous NADH was oxidized by oxygen with an optimum at pH 6.9. Under low-cation conditions, EGTA or EDTA (both 1 mM) had no effect on the Vmax. of NADH oxidation, although the removal of bivalent cations from the membrane surface by the chelators could be observed by use of 9-aminoacridine fluorescence. In contrast, under high-cation conditions, chelators lowered the Vmax. by about 50%, probably due to a better approach of the negatively charged chelators to the negative membrane surface than under low-cation conditions. In a low-cation medium, the Vmax. of NADH oxidation was increased by about 50% by the addition of cations. This was caused by a lowering of the size of the negative surface potential through charge screening. In contrast with other cations, La3+ inhibited NADH oxidation, possibly through binding to lipids essential for NADH oxidation. The apparent Km for NADH varied 6-fold in response to changes in the size of the surface potential, suggesting that the approach of the negatively charged NADH to the active site is hampered by the negative surface potential. The results demonstrate that the spinach leaf cell can regulate the mitochondrial NAD(P)H oxidation through several mechanisms: the pH; the cation concentration in general; and the concentration of Ca2+ in particular. The results also emphasize the importance of electrostatic considerations when investigating the kinetic behaviour of membrane-bound enzymes.     

Making transgenic livestock: genetic engineering on a large scale.

The feasibility of introducing foreign genes into the genomes of cattle, goats, pigs, and sheep has only recently been demonstrated. Studies have thus far focused on improving growth efficiency or directing expression of pharmaceutical proteins to the mammary glands of these species. The general strategy for producing transgenic livestock and mice is similar. In addition to the obvious difference in scale between mice and livestock experiments, there are noteworthy obstacles that significantly reduce the efficiency of producing transgenic livestock. Low embryo viability, low transgene integration rates, and high animal costs contribute to project costs that can easily exceed hundreds of thousands of dollars. A better understanding of the mechanisms that govern transgene integration should lead to improved efficiencies. But, the full potential of the transgenic livestock system will not be fully realized until: 1) gene constructs can be designed that function in a reproducible, predictable manner; and 2) the genetic control of physiological processes are more clearly elucidated. Newly emerging approaches may resolve at least some of these issues within the next decade.     

Preliminary phylogenetic analysis of the Protanisoptera (Insecta: Odonatoptera)

The Permian suborder Protanisoptera (Insecta: Odonatoptera) is revised and a new phylogenetic hypothesis proposed after analyses based on wing venation and different outgroups. After our study the families Camptotaxineuridae and Kaltanoneuridae are excluded from the Protanisoptera. After a new phylogenetic analysis, the family Permaeschnidae is redefined and the families Pholidoptilidae, Polytaxineuridae, Callimokaltaniidae and Hemizygopteridae are restored, as already proposed for the latter three families by Bechly (1996). The new genus Proditaxineura is described. The genus Gondvanoptilon RÖSLER et al., 1981 is excluded from the Meganisoptera: Erasipteridae and re-included in the Permaeschnidae, as already proposed by Bechly (1998). Permaeschna proxima MARTYNOV, 1931 is considered as a junior synonym of Permaeschna dolloi MARTYNOV, 1931. Pholidoptilon camense ZALESSKY, 1931 is excluded from Permaeschna MARTYNOV, 1931 and the genus Pholidoptilon [Zalessky, 1931a] and [Zalessky, 1931b] is restored. Ditaxineurella stigmalisMARTYNOV, 1940 is excluded from the Hemizygopteridae and considered as a Protanisoptera Incertae sedis.