The LIKE SEX FOUR 1-malate dehydrogenase complex functions as a scaffold to recruit ß-amylase to promote starch degradation.

In plant leaves, starch is composed of glucan polymers that accumulate in chloroplasts as the products of photosynthesis during the day; starch is mobilized at night to continuously provide sugars to sustain plant growth and development. Efficient starch degradation requires the involvement of several enzymes, including ß-amylase and glucan phosphatase. However, how these enzymes cooperate remains largely unclear. Here, we show that the glucan phosphatase LIKE SEX FOUR 1 (LSF1) interacts with plastid NAD-dependent malate dehydrogenase (MDH) to recruit ß-amylase (BAM1), thus reconstituting the BAM1-LSF1-MDH complex. The starch hydrolysis activity of BAM1 drastically increased in the presence of LSF1-MDH in vitro. We determined the structure of the BAM1-LSF1-MDH complex by a combination of cryo-electron microscopy, crosslinking mass spectrometry, and molecular docking. The starch-binding domain of the dual-specificity phosphatase and carbohydrate-binding module of LSF1 was docked in proximity to BAM1, thus facilitating BAM1 access to and hydrolysis of the polyglucans of starch, thus revealing the molecular mechanism by which the LSF1-MDH complex improves the starch degradation activity of BAM1. Moreover, LSF1 is phosphatase inactive, and the enzymatic activity of MDH was dispensable for starch degradation, suggesting nonenzymatic scaffold functions for LSF1-MDH in starch degradation. These findings provide important insights into the precise regulation of starch degradation.

Complete atrioventricular block due to timolol eye drops: a case report and literature review.

BACKGROUND: Timolol Maleate is a non-selective beta-adrenergic blocker that is commonly used to treat open-angle glaucoma. Despite its topical administration, ophthalmic timolol enters systemic circulation and produces a systemic beta-adrenergic blockade. We report a case of long-term timolol use that uncovered and worsened an underlying cardiac conduction defect demonstrated as a third degree atrioventricular (AV) block. CASE PRESENTATION: A 62-year old male with a 13-year history of glaucoma was hospitalized due to shortness of breath, dizziness, and amaurosis. Electrocardiography indicated a heart rate (HR) of 29 bpm with complete atrioventricular (AV) block, and the HR was significantly increased with the treatment of isoprenaline. However, the patient experienced bradycardic episodes (- 20 Δbpm) immediately after self-administration of timolol eye drops. The AV block and bradycardia resolved 48-h after timolol cessation. The man was discharged 1 week later with an asymptomatic first-degree A-V block. However, he presented with a worsened A-V block at his one-year checkup. CONCLUSION: We conclude that chronic topical timolol administration may aggravate a cardiac conduction defect leading to an AV block that is only temporarily resolved by timolol cessation. Patients taking timolol should be routinely monitored for cardiovascular aberrations and if any detected, immediately discontinue timolol therapy. Individuals experiencing timolol induced cardiovascular side effects should receive long term follow-up even if symptoms resolve, as they may be indicative of an underlying conduction defect.

[Effects of Green Manures on Soil Dissolved Organic Matter in Moisture Soil in North China].

Soil dissolved organic matter (DOM) plays an important role in the biogeochemistry of carbon, nitrogen, and phosphorus and in the transport of heavy metals and pesticides in soil. In moisture soil, green manures and soils were sampled in situ at the ploughed stage of green manures. A 56-day laboratory incubation experiment was conducted to simulate the dynamic changes of soil DOM influenced by the decomposition of green manures, the green manures were Hairy vetch (Vicia villosa Roth.), February orchid (Orychophragmus Violaceus L.), Rye (Secale cereale L.), the soil without green manure was used as a control (CK). The composition and ultraviolet-visible spectrum parameters of soil DOM were investigated at different incubation stages. Results showed that green manures could increase the dissolved organic carbon (DOC), the total organic acids (TOAs) and total carbohydrate (TCs) contents, and all treatments were reached a peak on the 1st day and decreased later. Hairy vetch affected DOC and TOAs most and were increased by 114.01% and 109.10% higher than CK respectively at the 1st and 14th day. Rye influenced the total carbohydrate (TCs) most and was maximumly 323.18% higher than CK at the 42nd day. Green manures could increase the dissolved organic nitrogen (DON) content, DON in all green manure treatments increased on the 1st day, decreased several days later and increased again after 20～30 d. Hairy vetch effected DON best and was 305.83% higher than CK at the 42nd day. All green manures increased in SUVA254, SUVA260, SUVA272, SUVA280 and SAUC240-400, while decreasing in A250/A365 and A240/A420. The PCA analysis of ultraviolet-visible spectrum parameters showed that SUVA254, SUVA260, SUVA272, SUVA280 had a high positive correlation between each other, and the same situation was found between A250/A365 and A240/A420. Among them, SAUC240-400 was a key factor parameter featuring the characteristics of DOM. The results suggested that green manures could increase the contents of DOM and its aromaticity, hydrophobic percentage, humification degree and average molecular weight, and could be increased and the stability of DOM could be enhanced accordingly. The ultraviolet-visible spectrum parameters could indicate the changes of characteristics of DOM in this study.

[Long-Term Different Fertilizations Changed the Chemical and Spectrum Characteristics of DOM of the Irrigation-Desert Soil in North-Western China].

By using Ultraviolet-visible Spectrometry, Fourier Transform Infrared Spectrometer and Elemental Analyzer, spectrum and chemical characteristics of soil DOM affected by long-term different fertilizations were investigated in irrigation-desert soil in North-western China based on an experiment started from 1988. Four different fertilization treatments were included, i. e., organic fertilizer (OF), green manure (GM), chemical fertilizer (CF) and a control of no fertilization (CK). The results showed that fertilization could increase the contents of DOM. Compared to CK, the treatments of OF, GM, CF increased the dissolved organic carbon (DOC) by 37%, 29%, 16%; increased the dissolved nitrogen (DON) by 334%, 257%, 182%; increased the total carbohydrate (TCs) by 90%, 25%, 2%; and increased the total organic acids (TOAs) by 195%, 116%, 58%; respectively. Furthermore, DOC, DON, TCs, and TOAs in the OF treatment were significantly higher than those in CK, they were also significantly higher in the GM and CF treatments except for TCs. The ultraviolet-visible analysis showed that fertilizations enhanced the SUVA(254), SUVA(260), SUVA(272) and SUVA(280) of DOM, indicating that fertilizations increased the aromatic and hydrophobic percentage, humification degree, and average molecular weight, and thus resulting in more stability of DOM. Same trends were showed for all the 4 ultraviolet spectrum absorption values in different fertilizations, i. e., the strongest effect was found in the OF treatment, and then was the GM treatment and CF treatment successively. From the results by the Fourier Transform Infrared Spectrometry, the characteristic peak of aromatic in the OF treatment was observed shifting from 1 625 to 1 649 cm(-1), which was close to the characteristic peak of humin, suggesting that the aromaticity of DOM in the OF treatment was higher than the other treatments. The characteristic peaks of C-O at 1 260-1 000 cm(-1) belonging to sugar, alcohol, and carboxylic acid were highest in the GM treatment, showing that the green manure could increase rich oxygen radicals. The highest characteristic peaks of N-H at 3 559, 3 419 and 1 456 cm(-1) were observed in the CF treatment, indicating that the chemical fertilizer could increase amine substances. The contents of C, O and N in the OF, GM, CF treatments were also increased respectively according to the elemental analysis.

Flow injection solid-phase extraction using multi-walled carbon nanotubes packed micro-column for the determination of polycyclic aromatic hydrocarbons in water by gas chromatography-mass spectrometry.

A flow injection solid-phase extraction preconcentration system using a multi-walled carbon nanotubes (MWCNTs) packed micro-column was developed for the determination of 16 polycyclic aromatic hydrocarbons (PAHs) in water by gas chromatography-mass spectrometry (GC-MS). The preconcentration of PAHs on the MWCNTs was carried out based on the adsorption retention of analytes by on-line introducing the sample into the micro-column system. Methanol was introduced to elute the retained analytes for GC-MS analysis using selected ion monitoring (SIM) mode. Important influence factors were studied in detail, such as sample acidity, sample flow rate, eluent flow rate and volume, dimensions of MWCNTs and amounts of packing material. Limits of detection of 16 PAHs for an extraction of 50 mL water sample were in the range of 0.001-0.15 microg L(-1), and the precisions (RSD) were in the range of 4-14%. The optimized method was successfully applied to the determination of 16 PAHs in surface waters, with recoveries in the range of 72-93% for real spiked sample.