There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

The reaction centers of PSI and PSII in chloroplast thylakoids are the major generation site of reactive oxygen species (ROS). Photoreduction of oxygen to hydrogen peroxide (H2O2) in PSI was discovered over 50 years ago by [Mehler (1951)][1]. Subsequently, the primary reduced product was identified

Production and scavenging of reactive oxygen species in chloroplasts and their functions.

Marked changes in socio-economic status, cultural traditions, population growth and agriculture are affecting diets worldwide. Understanding how our diet and nutritional status influence the composition and dynamic operations of our gut microbial communities, and the innate and adaptive arms of our immune system, represents an area of scientific need, opportunity and challenge. The insights gleaned should help to address several pressing global health problems.

/pdf/human-nutrition-the-gut-microbiome-and-the-immune-system-1cvm0c9gbb.pdf

Human nutrition, the gut microbiome and the immune system.

Tetrathiafulvalenes, oligoacenenes, and their buckminsterfullerene derivatives: the brick and mortar of organic electronics.

https://www.zora.uzh.ch/id/eprint/53843/1/H%C3%B6rtensteiner_BBA_2011.pdf

Chlorophyll breakdown in higher plants.

The biosynthetic pathway of Chl, probably the most important pigment in the biosphere, has been studied in considerable detail and is mentioned in plant physiology textbooks. Oddly enough, however, the breakdown of Chl is barely mentioned. Yet, as pointed out by Hendry et al. (1987), an estimated one billion tons of Chl are broken down every year, seemingly without leaving a trace. The only enzyme that is taught is chlorophyllase, discovered by Arthur Stoll in 1912, which cleaves Chl into phytol and Chlide, the Mg-porphyrin moiety of Chl. For most of the subsequent 80 years, chlorophyllase has been the only known part of the catabolic system. Until quite recently a11 the subsequent steps of Chlide breakdown remained undiscovered because no one was able to identify the breakdown products. We now know that the reason these products remained undetected is quite trivial: they are colorless. In mammals, the bile pigments biliverdin and bilirubin are colored breakdown products of heme; by analogy, plant biochemists may have expected the breakdown products of Chlide to be colored as well, but this is not the case, which is probably why they were overlooked for so long. The identification of the structures of these colorless catabolites has, in the last few years, led to the elucidation of the pathway of Chl catabolism in the senescing leaves of higher plants.

Chlorophyll Breakdown in Senescent Leaves.

During senescence, chlorophyll (chl) is metabolized to colorless nonfluorescent chl catabolites (NCCs). A central reaction of the breakdown pathway is the ring cleavage of pheophorbide (pheide) a to a primary fluorescent chl catabolite. Two enzymes catalyze this reaction, pheide a oxygenase (PAO) and red chl catabolite reductase. Five NCCs and three fluorescent chl catabolites (FCCs) accumulated during dark-induced chl breakdown in Arabidopsis (Arabidopsis thaliana). Three of these NCCs and one FCC (primary fluorescent chl catabolite-1) were identical to known catabolites from canola (Brassica napus). The presence in Arabidopsis of two modified FCCs supports the hypothesis that modifications, as present in NCCs, occur at the level of FCC. Chl degradation in Arabidopsis correlated with the accumulation of FCCs and NCCs, as well as with an increase in PAO activity. This increase was due to an up-regulation of Pao gene expression. In contrast, red chl catabolite reductase is not regulated during leaf development and senescence. A pao1 knockout mutant was identified and analyzed. The mutant showed an age- and light-dependent cell death phenotype on leaves and in flowers caused by the accumulation of photoreactive pheide a. In the dark, pao1 exhibited a stay-green phenotype. The key role of PAO in chl breakdown is discussed.

Chlorophyll breakdown in senescent Arabidopsis leaves. Characterization of chlorophyll catabolites and of chlorophyll catabolic enzymes involved in the degreening reaction.

https://chemistry-europe.onlinelibrary.wiley.com/doi/pdf/10.1002/chem.201490218

Cover Picture: Stereo‐ and Regioselective Phyllobilane Oxidation in Leaf Homogenates of the Peace Lily (Spathiphyllum wallisii): Hypothetical Endogenous Path to Yellow Chlorophyll Catabolites (Chem. Eur. J. 1/2015)

B12-cofactors play important roles in the metabolism of microorganisms, animals and humans. Microorganisms are the only natural sources of B12-derivatives, and the latter are “vitamins” for other B12-requiring organisms. Some B12-dependent enzymes catalyze complex isomerisation reactions, such as methylmalonyl-CoA mutase. They need coenzyme B12, an organometallic B12-derivative, to induce enzymatic radical reactions. Another group of widely relevant enzymes catalyzes the transfer of methyl groups, such as methionine synthase, which uses methylcobalamin as cofactor. This tutorial review covers structure and reactivity of B12-derivatives and structural aspects of their interactions with proteins and nucleotides, which are crucial for the efficient catalysis by the important B12-dependent enzymes, and for achieving and regulating uptake and transport of B12-derivatives.

Bernhard Kräutler

Papers

Chlorophyll breakdown in higher plants.

Chlorophyll Breakdown in Senescent Leaves.

Chlorophyll breakdown in senescent Arabidopsis leaves. Characterization of chlorophyll catabolites and of chlorophyll catabolic enzymes involved in the degreening reaction.

Cover Picture: Stereo‐ and Regioselective Phyllobilane Oxidation in Leaf Homogenates of the Peace Lily (Spathiphyllum wallisii): Hypothetical Endogenous Path to Yellow Chlorophyll Catabolites (Chem. Eur. J. 1/2015)

Vitamin B12-derivatives—enzyme cofactors and ligands of proteins and nucleic acids