Amplicons of maize zein genes are conserved within genic but expanded and constricted in intergenic regions

The properties are discussed of system y+L, a broad scope amino acid transporter which was first identified in human erythrocytes. System y+L exhibits two distinctive properties: (a) it can bind and translocate cationic and neutral amino acids, and (b) its specificity varies depending on the ionic composition of the medium. In Na+ medium, the half-saturation constant for L-lysine influx was 9.5 +/- 0.67 microM and the inhibition constant (Ki) for L-leucine was 10.7 +/- 0.72 microM. L-Leucine is the neutral amino acid that binds more powerfully, whereas smaller analogues, such as L-alanine and L-serine interact less strongly (the corresponding inhibition constants were Ki,Ala, 0.62 +/- 0.11 mM; Ki,Ser, 0.49 +/- 0.08 mM). In the presence of K+, the carrier functions as a cationic amino acid specific carrier, but Li+ is able to substitute for Na+ facilitating neutral amino acid binding. The effect of the inorganic cations is restricted to the recognition of neutral amino acids; translocation occurs at similar rates in the presence of Na+, K+ and Li+. The only structural feature that appears to impair translocation is bulkiness and substrates with half-saturation constants differing by more than 100-fold translocate at the same rate. This suggests that translocation is largely independent of the forces of interaction between the substrate and the carrier site. System y+L activity has been observed in Xenopus laevis oocytes injected with the cRNA for the heavy chain of the 4F2 human surface antigen. 4F2hc is an integral membrane protein with a single putative membrane-spanning domain and it remains to be clarified whether it is part of the transporter or an activator protein.     

Electronic and ionic transport in liquid PbO-SiO2 systems

The objective of the present work was to examine electronic transport in the PbO-SiO₂ melt. The experimental work consisted of studying the oxidation of liquid Pb covered by a layer of liquid PbO-SiO₂ using a thermogravimetric arrangement. Oxidation of liquid Pb was dependent on the melt height and was parabolic in nature, indicating the oxidation process to be diffusion controlled. We observed a moderate increase in the oxidation rate with additions of a transition metal oxide (Fe₂O₃) to the melt. However, when melt/gas and melt/metal interfaces were short circuited by Ir wires, a much higher increase in the oxidation rate was noticed. Additionally, the conductivity of the PbO-SiO₂ melt with Fe₂O₃ additions was measured as a function of P_o, to detect the nature of electronic contribution by the Fe₂O₃. Combining the results of the oxidation and conductivity experiments, we conclude that the oxidation of liquid lead covered by liquid slag occurs through ionic and rate controlling electronic (probably electron holes) transport in the melt. Uday Pal, formerly with the Department of Materials Science and Engineering, The Pennsylvania State University