Two forms of NADP-dependent malic enzyme in expanding maize leaves

Etiolated maize leaves (Zea mays L.) contain a major isozyme of NADP-dependent malic enzyme (L-malate dehydrogenase, decarboxylating, EC 1.1.1.40) having an isoelectric point of 5.28±0.03, a K_m (L-malate) 0.3–0.6 mM at pH 7.45; a broad pH optimum around pH 6.9 under the conditions of assay; a molecular weight of 280,000 (sometimes accompanied by a minor component of 150,000); and an NAD-dependent activity about 1/50 the NADP-dependent activity. This isozyme, resembling the NADP-malic enzyme of vertebrates, is labeled type 1. The dominant isozyme of young green leaves (type 2) has, however, a pI 4.90±0.03, a K_m (L-malate) 0.10–0.15 mM, a pH optimum of 8, and a molecular weight of 280,000. It is also more stable and exhibits an appreciable NAD-dependent activity (1/5–1/7 the NADP activity). Both isozymes show linear kinetics, dependence on Mn or Mg ions, similar K_m (NADP⁺), and the typical increase of K_m for L-malate with increasing pH values. Type 1 isozyme of maize is assumed to be cytosolic. Type 2 corresponds in each property to the chloroplast enzyme of bundle-sheath cells. It is present at a low level in etiolated leaves and develops to a high specific activity (up to 100 nmol min^-1 mg protein^-1 by 150 h illumination) during photosynthetic differentiation, replacing the type 1 form.Abbreviation MES 2 (N-morpholino)ethane sulfonic acid Work supported by grants from the Consiglio Nazionale delle Ricerche for years 1975 and 1976     

Modulation of Quinolinic and Kynurenic Acid Content in the Rat Brain: Effects of Endotoxins and Nicotinylalanine

Quinolinic acid, an endogenous excitotoxin, and kynurenic acid, an antagonist of excitatory amino acid receptors, are believed to be synthesized from tryptophan after the opening of the indole ring. They were measured in the rat brain and other organs using gas chromatography-mass spectrometry or HPLC. The enzyme indoleamine 2,3-dioxygenase, capable of cleaving the indole ring of tryptophan, was induced by administering bacterial endotoxins to rats, which significantly increased the brain content of both quinolinic and kynurenic acids. Nicotinylalanine, an analogue of kynurenine, inhibited this endotoxin-induced accumulation of quinolinic acid while potentiating the accumulation of kynurenic acid. The possibility of significantly increasing brain concentrations of kynurenic acid without a concomitant increase in quinolinic acid may provide a useful approach for studying the role of these electrophysiologically active tryptophan metabolites in brain function and preventing the possible toxic actions of abnormal synthesis of quinolinic acid.     

Higher alcohol and acetic acid production by apiculate wine yeasts

P. ROMANO, G. SUZZI, G. COMI AND R. ZIRONI. 1992. Ninety-six strains of apiculate wine yeasts were investigated for their ability to produce higher alcohols and acetic acid in synthetic medium. Less isoamyl alcohol and more n -propanol and isobutanol were formed by Hanseniaspora guilliermondii than by Kloeckera apiculata. The latter produced twice as much acetic acid as H. guilliermondii. The production of higher alcohols and acetic acid was found to be a characteristic of individual strains and was statistically significant. In a multivariate analysis of higher alcohol production two main groupings were formed at 86%S, corresponding to the taxa H. guilliermondii and K. apiculata. Strains that produced low amounts (50 mg/1) of acetic acid, comparable with that of Saccharomyces cerevisiae, were found in both species of apiculate yeasts.     

Single-stranded molecules in DNA preparations from cultured mammalian cells at different moments of cell cycle

Long single-stranded DNA molecules have been observed at electron microscope in DNA preparations from synchronized Chinese hamster cells. The amount of single strandedness in parental DNA increases following a prolonged block of DNA synthesis by hydroxyurea as judged by the results obtained using an improved hydroxyapatite chromatography (Hanania et al., 1975). As far as newly replicated DNA is concerned, an increase of the single strand amount has been observed in DNA preparations from cells actively synthesizing DNA.     

Lazy leukocyte syndrome.

A-35-year-old woman with a long-lasting history of neutropenia and recurrent infections was found to have defective neutrophil chemotaxis, random motility, and in vivo migration. Although the bone marrow granulocyte reserve was normal, the patient failed to release an appropriate amount of granulocytes after injection of etiocholanolone. These features are characteristic of the so-called "Lazy leukocyte syndrome". The clinical presentation of the five cases of this syndrome so far reported and its pathophysiological aspects are discussed.     

Effects of 50 Hz magnetic fields on mouse spermatogenesis monitored by flow cytometric analysis

Flow cytometry (FCM) was performed to monitor the cellular effects of extremely-low-frequency magnetic field on mouse spermatogenesis. Groups of five male hybrid F1 mice aged 8–10 weeks were exposed to 50 Hz magnetic field. The strength of the magnetic field was 1.7 mT. Exposure times of 2 and 4 h were chosen. FCM measurements were performed 7, 14, 21, 28, 35, and 42 days after treatment. For each experimental point, a sham-treated group was used as a control. The possible effects were studied by analyzing the DNA content distribution of the different cell types involved in spermatogenesis and using the elongated spermatids as the reference population. The relative frequencies of the various testicular cell types were calculated using specific software. In groups exposed for 2 h, no effects were observed. In groups exposed for 4 h, a statistically significant (P < 0.001) decrease in elongated spermatids was observed at 28 days after treatment. This change suggests a possible cytotoxic and/or cytostatic effect on differentiating spermatogonia. However, further studies are being carried out to investigate the effects of longer exposure times. © 1995 Wiley-Liss, Inc.     

Light controls stamen elongation via cryptochromes,phytochromes and COP1 through HY5 and HYH

In Arabidopsis, stamen elongation, which ensures male fertility, is controlled by the auxin response factor ARF8, which regulates the expression of the auxin repressor IAA19. Here, we uncover a role for light in controlling stamen elongation. By an extensive genetic and molecular analysis we show that the repressor of light signaling COP1, through its targets HY5 and HYH, controls stamen elongation, and that HY5 – oppositely to ARF8 – directly represses the expression of IAA19 in stamens. In addition, we show that in closed flower buds, when light is shielded by sepals and petals, the blue light receptors CRY1/CRY2 repress stamen elongation. Coherently, at flower disclosure and in subsequent stages, stamen elongation is repressed by the red and far‐red light receptors PHYA/PHYB. In conclusion, different light qualities – sequentially perceived by specific photoreceptors – and the downstream COP1–HY5/HYH module finely tune auxin‐induced stamen elongation and thus male fertility.