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Liver Diseases
Published in George Feuer, Felix A. de la Iglesia, Molecular Biochemistry of Human Disease, 2020
George Feuer, Felix A. de la Iglesia
The mechanism of the glucose effect has not been established. It may reflect a catabolite repression. Since there is no catabolite common in the pathways between glucose metabolism and heme synthesis, the catabolic repression is probably linked with cyclic AMP. The effect of glucose in porphyria is remarkably similar to the effect of glucose on the synthesis of cyclic AMP. The related δ-aminolevulinic acid synthetase formation is lowered by glucose because it represses the intracellular levels of cyclic AMP. Consequently, reduced levels of cyclic AMP reduce the rate of enzyme synthesis. The relationship of this effect to the disappearance of the neurological symptoms is not clear.
Consideration of Glutamine Synthetase as a Multifunctional Protein
Published in James F. Kane, Multifunctional Proteins: Catalytic/Structural and Regulatory, 2019
The proposal that glutamine synthetase is involved in the regulation of protein synthesis was based primarily on results with mutants of K. aerogenes. This section will review only a few of the critical results that led to this proposal; a more comprehensive review of these earlier investigations is available.35 The initial work dealt with the regulation of histidine utilization (hut) as a nitrogen source by K. aerogenes. It had been observed that histidase, the first enzyme for histidine degradation, was produced at higher levels in cells grown in a medium with glucose as a carbon source and histidine as a nitrogen source than in medium with glucose, ammonium, and histidine.36,37 Histidase activities decreased when a more rapidly utilizable nitrogen source was available and increased when higher activities of histidase were needed to use histidine as a nitrogen source. This response can be referred to as nitrogen control or nitrogen catabolite repression. The implication that glutamine synthetase functioned as a regulatory molecule during nitrogen control came from a number of studies. First, physiological experiments demonstrated that glutamine synthetase activities also increased in cells grown in a medium with a limiting nitrogen source such as histidine (Table 1), and in fact there was a direct correlation between glutamine synthetase and histidase activities for a variety of growth conditions.38,39 In contrast, the measurement of one of the glutamate synthesizing enzymes, glutamate dehydrogenase, showed that its activity consistently decreased whenever glutamine synthetase activities were high (see Table l).40,41 Because a second enzyme, glutamate synthase, exists that can produce glutamate during a nitrogen-limiting growth condition, glutamate dehydrogenase activities were not essential and could be repressed when K. aerogenes was growing in these media. Glutamine auxotrophs lacking an active glutamine synthetase were unable to increase histidase levels or reduce glutamate dehydrogenase levels when the cells were limited for a nitrogen source. In contrast, mutants with elevated glutamine synthetase activities also had higher induced levels of histidase and reduced glutamate dehydrogenase activities even when grown in a medium with high concentrations of ammonia.38–41
Cellulolytic bacteria in the large intestine of mammals
Published in Gut Microbes, 2022
Alicia Froidurot, Véronique Julliand
The existence of OMVs containing CAZymes and a fibro-slime complex has been demonstrated in F. succinogenes S85, which is a reference strain isolated from the bovine rumen.119 Recently, a potentially cellulolytic multiprotein complex of degradative enzymes and fibro-slimes was identified. This complex, anchored to the outer membrane peptidoglycan, is thought facilitate the adhesion of F. succinogenes S85 to cellulose and subsequent cellulose degradation. The up-regulation of these proteins in cellulose-grown cells also indicates that the expression of the corresponding genes is controlled by catabolite repression. Cyclic di-guanidine monophosphate, known to regulate a variety of functions, has been proposed to be involved in cellulose degradation.120
Phosphodiesterase 5 (PDE5) restricts intracellular cGMP accumulation during enterotoxigenic Escherichia coli infection
Published in Gut Microbes, 2020
Jennifer Foulke-Abel, Huimin Yu, Laxmi Sunuwar, Ruxian Lin, James M. Fleckenstein, James B. Kaper, Mark Donowitz
Measurement of intracellular cAMP and cGMP in HEMs colonized by H10407 was recently reported.24,26 However, the characterization of infection-associated cyclic nucleotide efflux has not been explored in the HEM model. Additionally, evaluation of an approximate pathophysiological ST concentration for experimental reference has not been described. In the present study, 108 cfu of log-phase H10407 were required to produce between 0.1 and 1 nM ST over an 8 h period, eliciting a modest cGMP response that is near the lower limits of detection by ELISA. Notably, earlier studies demonstrated that ST production is sensitive to catabolite repression by glucose27 and that ST production increases as the bacteria enter a stationary phase of growth.28 Thus, it is likely that the use of log-phase bacteria contributed to the inoculum required to elicit measurable cGMP response in the target epithelia. We verified that ST is unable to stimulate cGMP synthesis if administered basolaterally, consistent with apical localization of the receptor (guanylate cyclase C) and demonstrates that ST is unable to breach the mucosa from the serosal side. This necessitates the use of HEMs to conduct ST experiments and limits studies in 3-D enteroid culture due to limited apical access.
β-Hemolytic Streptococcus anginosus subsp. anginosus causes streptolysin S-dependent cytotoxicity to human cell culture lines in vitro
Published in Journal of Oral Microbiology, 2019
Atsushi Tabata, Takuya Yamada, Hiromi Ohtani, Kazuto Ohkura, Toshifumi Tomoyasu, Hideaki Nagamune
In S. pyogenes, it was reported that the cre sequence existed in the promoter region of the sag operon and it was suggested that the carbon catabolite repression contributed to the process of SLS production [30]. Recently, it has been reported that the SLS production from β-SAA is also regulated by the catabolite control protein CcpA [31]. These results suggest that the conditions for SLS production will be strongly affected by the environment in their habitats or infected sites. In addition, because our result showed that the SLS-dependent cytotoxicity of β-SAA is not high and is caused by a continuous action of secreted SLS (Figure 4), it is suggested that the cytotoxicity of β-SAA could be established by the continuous production of SLS at the infection sites of β-SAA. The AGS species including SAA is thought to be one of the opportunistic pathogens against humans and often escape from the human normal immune system to cause infection in vivo. Therefore, SLS may be a risk factor for infection caused not only by pyogenic streptococci such as S. pyogenes but also by the SLS-producing β-hemolytic sub-group of AGS. This prediction also suggests that suppression of SLS production or inactivation of SLS would help us to prevent the infective diseases caused by the SLS-producing AGS strains.