An Irreversible and Kinetically Controlled Process: Thermal Induced Denaturation of <Emphasis Type="SmallCaps">L</Emphasis>-2-Hydroxyisocaproate Dehydrogenase from <Emphasis Type="Italic">Lactobacillus confusus</Emphasis>

The thermal denaturation of Lactobacillus confusus l-2-Hydroxyisocaproate Dehydrogenase (l-HicDH) has been studied by Differential Scanning Calorimetry (DSC). The stability of this enzyme has been investigated at different pH conditions. The results of this study indicate that the thermal denaturation of this enzyme is irreversible and the T _m is dependent on the scan-rate, which suggests that the denaturation process of l-HicDH is kinetically determined. The heat capacity function of l-HicDH shows a single peak with the T _m values between 52.14°C and 55.89°C at pH 7.0 at different scan rates. These results indicate that the whole l-HicDH could unfold as a single cooperative unit, and intersubunit interactions of this homotetrameric enzyme must play a significant role in the stabilization of the whole enzyme. The rate constant of the unfolding is analyzed as a first order kinetic constant with the Arrhenius equation, and the activation energy has been calculated. The variation of the activation energy values obtained with different methods does not support the validity of the one-step irreversible model. The denaturation pathway was described by a three-state model, N → U → F, in which the dissociation of the tetramer takes place as an irreversible step before the irreversible unfolding of the monomers. The calorimetric enthalpy associated with the irreversible dissociation and the calorimetric enthalpy associated with the unfolding of the monomer were obtained from the best fitting procedure. Thermal unfolding of l-HicDH was also studied using Circular Dichroism (CD) spectroscopy. Both methods yielded comparable values.     

<Emphasis Type="SmallCaps">l</Emphasis>-Arginine Suppresses Aggregation of Recombinant Growth Hormones in Refolding Process from <Emphasis Type="Italic">E. coli</Emphasis> Inclusion Bodies

l-Arginine was used to suppress the aggregation of recombinant mink and porcine growth hormones in the refolding process from E. coli inclusion bodies by solubilization–dilution protocol at high protein concentration and pH 8.0. The influence of l-arginine concentration on the renaturation yield of both proteins was investigated. l-Arginine effectively suppressed the precipitation of growth hormones during dilution, but did not inhibit soluble oligomers formation. The results of mink and porcine growth hormones purification from 4 g of biomass are presented.     

The Current Status of Preclinical Endocrine Education in U.S. Medical Schools

ObjectiveTo characterize the current landscape of preclinical medical endocrine education in U.S. allopathic medical schools.MethodsU.S. endocrine curriculum directors were asked to voluntarily complete a 16-question email survey surveying the status of endocrine preclinical education at their medical school.ResultsSixty-nine of 155 (45%) endocrine block director respondents completed the online survey between July 2021 and September 2021. A larger incoming class, a longer duration of the endocrine curriculum, and the offering of a separate endocrine curriculum (ie apart from the teaching of other organ systems) were each independently associated with an increased number of faculty teaching the course. Schools that used a gland-/organ-based curriculum only and those that used a combination of gland-/organ-based curriculum with topic-based curriculum differed significantly in their use of large lectures, small groups, and several curriculum components, including point of care glucose testing, continuous glucose monitoring, and insulin pumps.ConclusionThis survey study reports the current landscape of preclinical endocrine education in the United States and describes opportunities to improve interest in pursuing endocrinology as a career.     

高校新型植物标本馆的建立与发展——以河南农业大学植物标本馆为例

高校标本馆作为重要的科普和教学实践基地,是连接大学与社会的桥梁,在提升高校社会影响力和加快高校发展中起着重要作用。目前,高校标本馆普遍存在经费少和缺乏管理等问题。如何立足高校现状,有效解决标本采集和标本数字化过程中耗时耗力的难题,建设具有地方特色的新型植物标本馆,是高校标本馆建设关注的焦点之一。该文以河南农业大学植物标本馆新馆建设为例,介绍了河南农业大学标本馆成立以来,充分发挥高校的人力资源优势,让学生通过实验课或野外实习积极参与新型植物标本馆的建设,基本实现了标本采集、制作、鉴定和数字化的同步进行。在这一过程中,既有效锻炼了学生能力,加深了学生对植物形态的认识,发挥了植物标本馆在教学、科学研究及科学普及中的积极作用,又极大地丰富了标本馆馆藏量,有效地促进了高校新型植物标本馆的发展。     

Importance of an appropriate visual presentation for avoiding a misconception of the menstrual cycle

Family planning, the prevention of unwanted pregnancy, and women’s reproductive health are topics that have received close attention for decades. It would therefore be fair to assume that there exists a good knowledge of the menstrual cycle. However, it is clear that many people have various misconceptions about the menstrual cycle and fertile days or ovulation, and that this process is still largely taught with the aid of materials and images that have not changed for many years. We investigated the effect of moving away from the usual teaching practice of using a 28-day diagram showing ovulation on the 14th day. A total of 184 students from three different high schools, aged between 17 and 18, participated in this research. The students who were taught using three diagrams showing different durations of the menstrual cycle showed a significantly better adoption of the facts and concepts compared to the students who were taught using a diagram of the average 28-day cycle. Our results confirmed that it is highly important to use appropriate visual displays in the teaching of the menstrual cycle and that it is essential to enhance the visual literacy of students and teachers.     

农林院校生物信息学专业数据库技术课程教学改革刍议

生物信息学是一门交叉学科,对于现代生物学研究具有重要的意义。数据库技术是生物信息学的基础之一。本文对农林院校的生物信息学专业的数据库技术课程的教学现状做了一些介绍,对目前生物信息专业数据库教学存在的问题进行了分析。结合教学的实践,有针对性的提出了一些教学改革的具体措施。     

An antitumor promoter from Moringa oleifera Lam.

In the course of studies on the isolation of bioactive compounds from Philippine plants, the seeds of Moringa oleifera Lam. were examined and from the ethanol extract were isolated the new O-ethyl-4-(α- -rhamnosyloxy)benzyl carbamate (1) together with seven known compounds, 4(α- -rhamnosyloxy)-benzyl isothiocyanate (2), niazimicin (3), niazirin (4), β-sitosterol (5), glycerol-1-(9-octadecanoate) (6), 3-O-(6′-O-oleoyl-β- -glucopyranosyl)-β-sitosterol (7), and β-sitosterol-3-O-β- -glucopyranoside (8). Four of the isolates (2, 3, 7, and 8), which were obtained in relatively good yields, were tested for their potential antitumor promoting activity using an in vitro assay which tested their inhibitory effects on Epstein–Barr virus-early antigen (EBV-EA) activation in Raji cells induced by the tumor promoter, 12-O-tetradecanoyl-phorbol-13-acetate (TPA). All the tested compounds showed inhibitory activity against EBV-EA activation, with compounds 2, 3 and 8 having shown very significant activities. Based on the in vitro results, niazimicin (3) was further subjected to in vivo test and found to have potent antitumor promoting activity in the two-stage carcinogenesis in mouse skin using 7,12-dimethylbenz(a)anthracene (DMBA) as initiator and TPA as tumor promoter. From these results, niazimicin (3) is proposed to be a potent chemo-preventive agent in chemical carcinogenesis.     

Enzymatic synthesis of lysophosphatidic acid and phosphatidic acid

Immobilised 1,3-specific lipase from Rhizopus arrhizus was used as catalyst for the esterification of -glycero-3-phosphate and fatty acid or fatty acid vinyl ester in a solvent-free system. With lauric acid vinyl ester as acyl donor, a_w<0.53 favored the synthesis of lysophosphatidic acid (1-acyl-rac-glycero-3-phosphate, LPA1) and the spontaneous acyl migration of the fatty acid on the molecule. Subsequent acylation by the enzyme resulted in high phosphatidic acid (1,2-diacyl-rac-glycero-3-phosphate, PA) formation and high total conversions (>95%). With oleic acid, maximum conversions of 55% were obtained at low water activities. Temperatures below melting point of the product favored precipitation and resulted in high final conversion and high product ratio [LPA/(PA+LPA)]. Thus, LPA was the only product with lauric acid vinyl ester as acyl donor at 25°C. Increased substrate ratio ( -glycero-3-phosphate/fatty acid) from 0.05 to 1 resulted in a higher ratio of LPA to PA formed, but a lower total conversion of -glycero-3-phosphate. Increased amounts of enzyme preparation did not result in higher esterification rates, probably due to high mass-transfer limitations.     

The alternative<Emphasis Type="SmallCaps"> d</Emphasis>-galactose degrading pathway of<Emphasis Type="Italic"> Aspergillus nidulans</Emphasis> proceeds via<Emphasis Type="SmallCaps"> l</Emphasis>-sorbose

The catabolism of d-galactose in yeast depends on the enzymes of the Leloir pathway. In contrast, Aspergillus nidulans mutants in galactokinase (galE) can still grow on d-galactose in the presence of ammonium—but not nitrate—ions as nitrogen source. A. nidulans galE mutants transiently accumulate high (400 mM) intracellular concentrations of galactitol, indicating that the alternative d-galactose degrading pathway may proceed via this intermediate. The enzyme degrading galactitol was identified as l-arabitol dehydrogenase, because an A. nidulans loss-of-function mutant in this enzyme (araA1) did not show NAD⁺-dependent galactitol dehydrogenase activity, still accumulated galactitol but was unable to catabolize it thereafter, and a double galE/araA1 mutant was unable to grow on d-galactose or galactitol. The product of galactitol oxidation was identified as l-sorbose, which is a substrate for hexokinase, as evidenced by a loss of l-sorbose phosphorylating activity in an A. nidulans hexokinase (frA1) mutant. l-Sorbose catabolism involves a hexokinase step, indicated by the inability of the frA1 mutant to grow on galactitol or l-sorbose, and by the fact that a galE/frA1 double mutant of A. nidulans was unable to grow on d-galactose. The results therefore provide evidence for an alternative pathway of d-galactose catabolism in A. nidulans that involves reduction of the d-galactose to galactitol and NAD⁺-dependent oxidation of galactitol by l-arabitol dehydrogenase to l-sorbose.     

Expression of a novel yeast gene that detoxifies the proline analog azetidine-2-carboxylate confers resistance during tobacco seed germination,callus and shoot formation

A novel acetyltransferase (Mpr1) found in Saccharomyces cerevisiae (strain 1278b) has been shown to specifically detoxify a proline analog, l-azetidine-2-carboxylic acid (A2C) in yeast cells [M. Shichiri et al. (2001) J Biol Chem 276: 41998–42002]. We investigated whether the yeast MPR1 gene would function similarly in a plant system and if its expression could confer resistance to proline analogs. The MPR1 gene coding sequence driven by two different constitutive promoters, with or without the 5- and 3-noncoding sequence from the MPR1 gene adjacent to the conventional NOS terminator, was transformed into tobacco (Nicotiana tabacum L. cv. Xanthi) plants via Agrobacterium tumefaciens infection. The presence of the yeast 5- and 3-noncoding sequences appeared to increase the likelihood of MPR1 gene expression in the transgenic plants. The kanamycin-selected transgenic plants with a high level of Mpr1 activity grew normally, and their progeny expressed acetyltransferase activity that could utilize A2C, azetidine-3-carboxylic acid and 4-hydroxy-l-proline as substrates. Resistance to A2C, but not to the other two analogs, was exhibited during leaf tissue culture and seed germination. The A2C toxicity to the wild-type plants was reversed by the addition of proline, suggesting that A2C acts as a proline analog. Our studies confirm that MPR1 can function in a similar fashion in tobacco as in yeast to detoxify the toxic proline analog A2C, so it could potentially be used as a new selectable marker for plant transformation. However, our attempts to utilize MPR1 as an efficient selectable marker gene for the A. tumefaciens-mediated transformation of tobacco were unsuccessful.Abbreviations A2C: l-Azetidine-2-carboxylic acid - A3C: Azetidine-3-carboxylic acid - Hyp: 4-Hydroxy-l-proline - hpt: Hygromycin phosphotransferase II - NPTII: Neomycin phosphotransferase II Communicated by H. Wang