An inquiry into the selective protection of glycine during the radiolysis of glycine-alanine mixtures in aqueous solutions and its implications to the preservation of optically active amino acids in the early earth

Akaboshi et al. (1990) has found an unexpected protection of the achiral amino acid, glycine, towards ionizing radiation at the expense of the selective destruction of the chiral amino acids, alanine and aspartic acid. The present work examines the mechanism of this protection for the case of alanine. We have developed a computer model for the radiolysis of glycine, alanine and glycine-alanine mixtures in aqueous solution. It is established that this protection is due in part to the reaction of the α-radical of glycine with alanine to regenerate a more stable α-radical, according to the following reaction, $$ \cdot CH(NH_3^ + )CO_2^ - + CH_3 CH(NH_3^ + )CO_2^ - \to CH_2 (NH_3^ + )CO_2^ - + CH_3 \dot C(NH_3^ + )CO_2^ -$$ The rate constant of this reaction was estimated to be ≤10⁴M^-1s^-1. The implications for this selective protection of glycine are considered for a hypothetical case in which there would be an enrichment of about 10% ofL-alanine in the primitive ocean and taking the glycine/alanine ratios obtained in CH₄-and CO₂- dominated atmospheres using electric discharge experiments. It is predicted that alanine would be rapidly destroyed and radioracemized in spite of the fact that the concentration of alanine is equal or significantly lower than that of glycine. Assuming that chiral amino acids were a prerequisite for the origin of life, it can be deduced that life could have appeared in a relatively short period of time unless there was a constant supply of optical amino acids from extraterrestrial sources.     

Influence of 2,4-d and lactose on pollen embryogenesis in anther culture of potato

Anthers of diploid genotypes of Solanum tuberosum capable of androgenesis were cultured on different media to examine the effect on induction of pollen embryogenesis of 2,4-d and lactose. Anthers cultured in callogenic medium with 2,4-d and sucrose produced pollen derived embryoids only exceptionally. When sucrose was replaced by lactose the frequency of embryogenesis was as high or higher than in embryogenic auxin-free medium. Substitution of lactose for sucrose in the embryogenic medium had no effect. Supplementing the embryogenic medium with 2,4-d strongly reduced the frequency of pollen embryoids in the presence of sucrose but not with lactose.Abbreviations 2,4-d 2,4-dichlorophenoxyacetic acid     

Deoxynivalenol and contaminant mycoflora in freshly harvested Argentinian wheat in 1993

A mycological survey was carried out on wheat heads from the main production area of Argentina. The isolation frequency and relative density of species from genus Fusarium and dematiaceous fungi were calculated. F graminearum was the predominant Fusarium species; similar to that observed in the USA and Canada. An analysis of deoxynivalenol (DON) natural contamination also was performed on a limited number (44) of samples. DON contamination levels in positive samples ranged from 0.2 to 30 ppm. A stepwise regression procedure showed that, among the species analysed, F. graminearum relative density was related to the DON contamination level and that other prevalent fungi did not influence or modify that relationship.     

Candida biotypes in patients with oral leukoplakia and lichen planus

Prevalence of yeasts in 35 leukoplakia and 34 oral lichen planus patients was compared with that observed in persons without oral diseases. Serotype and morphotype were determined on Candida albicans isolates. Yeasts were isolated from the oral cavity specimens of 43.7% of the patients. C. albicans (serotype A) was the predominant species (76% in leukoplakia, 88.2% in lichen planus and 60.8% in healthy persons). Sixteen morphotypes were encountered on malt extract agar, being 732, 733, 734, 753 and 754 the most frequently found. Morphotypes SP1N and SP1Y were the most common on Sabouraud-trypheniltetrazolium agar (68.4% of the isolates from leukoplakia and 73.3% from lichen planus, but only 46.6% of the isolates from healthy oral mucosa showed SP1N morphotype). Presence of oral lesions was associated with a marked reduction in the yeast species and C. albicans biotypes, suggesting that C. albicans and particularly some of its biotypes, show a high potential of adaptation to the changes associated with the development of oral leukoplakia and lichen planus.     

Mixed connective tissue disease. A clinico-serological study of 17 cases

Mixed connective tissue disease (MCTD) was described as a distinct clinical syndrome in 1972. Since then many cases have been reported in the literature worldwide. In this study we present our experience with a group of 17 Mexican patients with this syndrome, and we analyze their clinical and serological features, as well as the causes of death in these patients. The patients are Mexican mestizos living in Guadalajara and most of them have been followed-up at Hospital General de Occidente for a period of 1–10 years. The female/male ratio was 16:1, and their age ranged from 14–55 years with a mean of 29 years. The disease duration has ranged from 1–17 years, with a mean of 6 years. Among the clinical manifestations we have found a high frequency of lymphadenopathy when compared with published series (13/17 or 76%), and the laboratory findings in our patients included a very high polyclonal increase of gammaglobulins (93%), lymphopenia (76%), direct immunofluorescence speckled nuclear epidermal deposits in skin biopsies (75%) and positive rheumatoid factor (65%). Other clinical and serological features were similar to those reported in other series of patients with MCTD. Six of the 17 patients have died (35%), and in 3 of them (17.5%) the cause of death was due to an infectious disease that suddenly presented, and apparently was not related to a concomitant high dose of steroids or malnutrition in the patients. It seems that in addition to the already well known autoimmune abnormalities that occur in MCTD, there are other features like the presence of lymphadenopathy, the high polyclonal increase of gammaglobulins, and the lymphopenia, that reflect the profound disturbance of the immune system in this syndrome, possibly contributing to the sudden appearance of a severe infectious disease in some of our patients.Abbreviations ANA antinuclear antibody - CIE counterimmunoelectrophoresis - MCTD mixed connective tissue disease - PHA passive hemagglutination - PM polymyositis - RF rheumatoid factor - SLE systemic lupus erythematosus - SS systemic sclerosis (SS)     

Hardening by abscisic acid of tobacco plantlets grownin vitro

Tobacco plantlets were grownin vitro on Murashige and Skoog’s medium with2 % of saccharose. Addition of 0.01 mM abscisic acid (ABA) into the medium decreased stomatal conductance of the adaxial epidermis and especially the abaxial epidermis without negative effects on growth parameters. As a result the rate of water loss from ABA-treated plantlets taken out of cultivation vessels was slower than that of control plantlets. This could help their acclimation after transplantation toex vitro conditions.     

The effect of virus infection on morphology and protein components of pollen grains

Morphology of pollen grains collected from healthy and virus infected plants ofChenopodium quinoa L.,Chenopodium album L. andNicotiana tabacum L. cv. Samsun was investigated using scanning electron microscopy (SEM). Pollen grains from tobacco plans infected with tobacco mosaic virus (TMV) were smaller, with rounded shape and conspicuous deformation of aperture unlike oval and smooth pollen grains from healthy plants. No morphological alterations were observed inC. quinoa andC. album plants infected with TMV and cucumber mosaic virus (CMV). Polyacrylamide gel electrophoresis of pollen proteins revealed substantial quantitative and qualitative differences in protein components of pollen grains collected from healthy and virus infected plants     

Comparison of the solution and crystal conformations of (G + C)-rich fragments of DNA.

DNA fragments crystallize in an unpredictable manner, and relationships between their crystal and solution conformations still are not known. We have studied, using circular dichroism spectroscopy, solution conformations of (G + C)-rich DNA fragments, the crystal structures of which were solved in the laboratory of one of the present authors. In aqueous trifluorethanol (TFE) solutions, all of the examined oligonucleotides adopted the same type of double helix as in the crystal. Specifically, the dodecamer d(CCCCCGCGGGGG) crystalized as A-DNA and isomerized into A-DNA at high TFE concentrations. On the other hand, the hexamer d(CCGCGG) crystallized in Z-form containing tilted base pairs, and high TFE concentrations cooperatively transformed it into the same Z-form as adopted by the RNA hexamer r(CGCGCG), although d(CCGCGG) could isomerize into Z-DNA in the NaCl + NiCl2) aqueous solution. The fragments crystallizing as B-DNA remained B-DNA, regardless of the solution conditions, unless they denatured or aggregated. Effects on the oligonucleotide conformation of 2-methyl-2,4-pentanediol and other crystallization agents were also studied. 2-Methyl-2,4-pentanediol induced the same conformational transitions as TFE but, in addition, caused an oligonucleotide condensation that was also promoted by the other crystallization agents. The present results indicate that the crystal double helices of DNA are stable in aqueous TFE rather than aqueous solution.     

A comparative study of the purity, enzyme activity, and inactivation by hydrogen peroxide of commercially available horseradish peroxidase isoenzymes A and C

Horseradish peroxidase (HRP) is a commercially important enzyme that is available from a number of supply houses in a variety of grades of purity and isoenzymic combinations. The present article describes a comparative study made on nine HRP preparations. Six of these samples were predominantly composed of basic HRP, pl 8.5, and three of acidic HRP, pl 3.5. Two of the basic preparations were of lower purity than the others. The apparent molar catalytic activity of basic HRP with 0.5 mMABTS and 0.2 mM H(2)O(2) was around 950 s(-1) (about 770 s(-1) for the less pure samples) and with a 5 mM guaiacol and 0.6 mM H(2)O(2) was about 180 s(-1) for all the samples. A similar value (approximately 1000 s(-1)) was observed for acidic HRP but only at higher concentrations of ABTS (20 mM). With 20 mM guaiacol the molar catalytic activity of the acid isoenzyme was 65 s(-1). The apparent K(M) for ABTS of the acidic isoenzyme was 4 mM whereas for the basic isoenzyme it was 0.1 mM. All the enzymes were inactivated by H(2)O(2) when it was supplied as the only substrate. Under these conditions the partition ratio (r = number of catalytic cycles given by the enzyme before its inactivation), apparent dissociation constant (K(l)), and apparent rate constant of inactivation (k(inact)) were about twice as large for the acidic samples (1350, 2.6 mM, 9 . 10(-3) s(-1)) as for the basic (650, 1.3 mM, 5 . 10(-3) s(-1)). The apparent catalytic constant (k(cat)) was 3-4 times larger, and the efficiency of catalysis (k(cat)/K(l)) was double for the acidic isoenzyme, but the efficiency of inactivation (k(inact)/K(l)) was similar. The data obtained provide useful information for those using HRP isoenzymes for biotechnological applications (e.g., biosensors, bioreactors, or assays). (c) 1996 John Wiley & Sons, Inc.