The authors review the available evidence supporting the possible role of oxidative stress in cataract formation from an epidemiological and a clinical point of view. They discuss in more detail what is presently known about the molecular mechanisms of response of the mammalian lens to an oxidative insult and report unpublished data on gene modulation upon oxidative stress in a bovine lens model. Main research endeavors that seem to be a most promising source of new insights into the problem of age-related cataract formation are briefly discussed.

S-allantoin, a major ureide compound, is produced in plant peroxisomes from oxidized purines. Sequence evidence suggested that the Transthyretin-like (TTL) protein, which interacts with brassinosteroid receptors, may act as a bifunctional enzyme in the synthesis of S-allantoin. Here, we show that recombinant TTL from Arabidopsis thaliana catalyzes two enzymatic reactions leading to the stereoselective formation of S-allantoin, hydrolysis of hydroxyisourate through a C-terminal Urah domain, and decarboxylation of 2-oxo-4-hydroxy-4-carboxy-5-ureidoimidazoline through an N-terminal Urad domain. We found that two different mRNAs are produced from the TTL gene through alternative use of two splice acceptor sites. The corresponding proteins differ in the presence (TTL 12 ) and the absence (TTL 22 ) of a rare internal peroxisomal targeting signal (PTS2). The two proteins have similar catalytic activity in vitro but different in vivo localization: TTL 12 localizes in peroxisomes, whereas TTL 22 localizes in the cytosol. Similar splice variants are present in monocots and dicots. TTL originated in green algae through a Urad-Urah fusion, which entrapped an N-terminal PTS2 between the two domains. The presence of this gene in all Viridiplantae indicates that S-allantoin biosynthesis has general significance in plant nitrogen metabolism, while conservation of alternative splicing suggests that this mechanism has general implications in the regulation of the ureide pathway in flowering plants.

we isolated a novel gene that is selectively induced both in roots and shoots in response to sulfur starvation. This gene encodes a cytosolic, monomeric protein of 33 kD that selectively binds NADPH. The predicted polypeptide is highly homologous ( > 70%) to leguminous isoflavone reductases (IFRs), but the maize protein (IRL for isoflavone reductase-like) belongs to a novel family of proteins present in a variety of plants. Anti-IRL antibodies specifically recognize IFR polypeptides, yet the maize protein is unable to use various isoflavonoids as substrates. IRL expression is correlated closely to glutathione availability: it is persistently induced in seedlings whose glutathione content is about fourfold lower than controls, and it is down-regulated rapidly when control levels of glutathione are restored. This glutathione-dependent regulation indicates that maize IRL may play a crucial role in the establishment of a thiol-independent response to oxidative stress under glutathione shortage conditions.

Two novel, structurally and functionally distinct phosphatases have been identified through the functional complementation, by maize cDNAs, of an Escherichia coli diphosphonucleoside phosphatase mutant strain. The first, ZmDP1, is a classical Mg 2؉ -dependent and Li ؉ -sensitive diphosphonucleoside phosphatase that dephosphorylates both 3-phosphoadenosine 5-phosphate (3-PAP) and 2-PAP without any discrimination between the 3-and 2-positions. The other, ZmDP2, is a distinct phosphatase that also catalyzes diphosphonucleoside dephosphorylation, but with a 12-fold lower Li ؉ sensitivity, a strong preference for 3-PAP, and the unique ability to utilize double-stranded DNA molecules with 3-phosphate-or 3-phosphoglycolate-blocking groups as substrates. Importantly, ZmDP2, but not ZmDP1, conferred resistance to a DNA repairdeficient E. coli strain against oxidative DNA-damaging agents generating 3-phosphate-or 3-phosphoglycolateblocked single strand breaks. ZmDP2 shares a partial amino acid sequence similarity with a recently identified human polynucleotide kinase 3-phosphatase that is thought to be involved in DNA repair, but is devoid of 5-kinase activity. ZmDP2 is the first DNA 3-phosphoesterase thus far identified in plants capable of converting 3-blocked termini into priming sites for reparative DNA polymerization. Diphosphonucleoside phosphatases (DPNPases)1 catalyze the conversion of diphosphonucleosides such as 3Ј-phosphoadenosine 5Ј-phosphate (3Ј-PAP) into their 5Ј-monophosphorylated derivatives (5Ј-AMP). They are ubiquitous among prokaryotes and eukaryotes and belong to a superfamily of Mg 2ϩ -dependent, lithium-sensitive phosphohydrolases, which also includes fructose-1,6-bisphosphate 1-phosphatase and various inositol-polyphosphate phosphatases. The prototype of prokaryotic DPNPases is the product of the Escherichia coli gene cysQ, which, if mutated, abolishes the capacity of bacterial cells to grow on sulfate as the sole source of sulfur (1). The first eukaryotic DPNPase to be isolated was the Li ϩ -and Na ϩ -sensitive enzyme encoded by the Saccharomyces cerevisiae gene HAL2 (2). By preventing the accumulation of 3Ј-PAP, an inhibitory side product generated upon reduction of 3Ј-phosphoadenosine 5Ј-phosphosulfate (3Ј-PAPS) to sulfite, the Hal2p phosphatase controls the flux of sulfate along the sulfur assimilation pathway (3). Because of the blockage of sulfur assimilation and the concomitant methionine auxotrophy caused by PAP accumulation under conditions of salt-inhibited Hal2p, this enzyme is considered a specific target of salt toxicity (4). During the last few years, various Li ϩ -sensitive phosphatases, all capable of restoring the ability of a yeast hal2/met22 mutant to grow on sulfate as the sole source of sulfur, have been identified in fungi, plants, and mammals (5-11). Despite the widespread occurrence of PAPS as an activated sulfate derivative for assimilatory sulfate reduction or sulfation reactions, the main metabolic scope of PAP hydrolysis by microbial or higher eukaryotic DPNPases is diffe...

We have studied the expression of the a-amylase, trypsin, and elastase II genes in the acinar pancreas during mouse development. Transcriptional control is the major mechanism by which the differential accumulation of ac-amylase, trypsin, and elastase II mRNAs is determined during late embryogenesis. The synthesis of pancreatic mRNAs is detected around day 15 of gestation and involves most if not all acinar cells. The DNA-binding activity of the pancreas-specific transcription factor PTF1, which binds to enhancers of genes expressed in this tissue, is detected for the first tiime at day 15 of gestation. The appearance of the factor at this early stage of development suggests that it plays an important role during pancreas differentiation.