The Arabidopsis thaliana L. genome contains 58 membrane proteins belonging to the mitochondrial carrier family. Two mitochondrial carrier family members, here named AtNDT1 and AtNDT2, exhibit high structural similarities to the mitochondrial nicotinamide adenine dinucleotide (NAD ؉ ) carrierScNDT1 from bakers' yeast. Expression of AtNDT1 or AtNDT2 restores mitochondrial NAD ؉ transport activity in a yeast mutant lacking ScNDT. Localization studies with green fluorescent protein fusion proteins provided evidence that AtNDT1 resides in chloroplasts, whereas only AtNDT2 locates to mitochondria. Heterologous expression in Escherichia coli followed by purification, reconstitution in proteoliposomes, and uptake experiments revealed that both carriers exhibit a submillimolar affinity for NAD ؉ and transport this compound in a counterexchange mode. Among various substrates ADP and AMP are the most efficient counter-exchange substrates for NAD ؉ .Atndt1-and Atndt2-promoter-GUS plants demonstrate that both genes are strongly expressed in developing tissues and in particular in highly metabolically active cells. The presence of both carriers is discussed with respect to the subcellular localization of de novo NAD ؉ biosynthesis in plants and with respect to both the NAD ؉ -dependent metabolic pathways and the redox balance of chloroplasts and mitochondria.Nucleotides are metabolites of enormous importance for all living cells. They are the essential building blocks for DNA and RNA synthesis, energize most anabolic and many catabolic reactions, and fulfill critical functions in intracellular signal transduction (1, 2). Moreover, nucleotides serve as cofactors for a wide number of enzymes and are, with water, the most highly connected compounds within the metabolic network (3). Among these co-factors nicotinamide adenine dinucleotides are widely used for reductive/oxidative processes, playing important roles in the operation and control of a wide range of dehydrogenase activities. Accordingly, nucleotides are essential in nearly all cell organelles, and transport of these solutes into mitochondria, plastids, the endoplasmic reticulum, the Golgi apparatus, and peroxisomes has been observed (4 -7).Two types of nucleotide transport proteins have been identified to date at the molecular level: nucleotide transporter (NTT) 2 type carriers and members of the mitochondrial carrier family. The former transporters occur in plastids from all plants (8) and in a limited number of intracellular pathogenic bacteria (9). Most NTT-type carrier proteins catalyze an ATP/ADPϩP i counter-exchange mode of transport (10 -13), but several bacterial NTT proteins mediate either H ϩ /nucleotide transport or NAD ϩ /ADP counter-exchange (12,14,15). With the exception of the bacterial NAD ϩ /ADP carrier (14), all NTT proteins exhibit 12 predicted trans-membrane domains, whereas none of the NTT proteins share structural or domain similarities to members of the mitochondrial carrier family (11).Carriers belonging to the mitochondrial carrier family (MC...

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Silicon carbide (SiC) samples have been joined by a pressureless slurry based method. The CaO-Al 2 O 3 (CA) glass-ceramic joining material has been characterized in term of crystalline phases and thermal and mechanical properties. A torsion test based on miniaturized hourglass shaped specimens has been used as pure shear strength test method for joined ceramic samples. Torsion results are compared to those obtained by a single lap offset (SLO) test in compression on the same joined materials. Pure shear strength of 104 ± 25 MPa has been measured by torsion test, whereas single lap offset gave 36 ± 8 MPa.*monica.ferraris@polito.it