scholarly journals An overview of ?-hydroxybutyrate catabolism: The role of the cytosolic NADP+-dependent oxidoreductase EC 1.1.1.19 and of a mitochondrial hydroxyacid-oxoacid transhydrogenase in the initial, rate-limiting step in this pathway

1991 ◽  
Vol 16 (9) ◽  
pp. 965-974 ◽  
Author(s):  
Elaine E. Kaufman ◽  
Thomas Nelson
Keyword(s):  
Initial Rate ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

scholarly journals Aldol Condensation of Cyclopentanone on Hydrophobized MgO. Promotional Role of Water and Changes in the Rate-Limiting Step upon Organosilane Functionalization

ACS Catalysis ◽  
2019 ◽  
Vol 9 (4) ◽  
pp. 2831-2841 ◽  
Author(s):  
Duong T. Ngo ◽  
Qiaohua Tan ◽  
Bin Wang ◽  
Daniel E. Resasco
Keyword(s):  
Aldol Condensation ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

Daily prolactin pulse inhibits the corpus luteum during lactational quiescence in the marsupial, Macropus eugenii

2013 ◽  
Vol 25 (2) ◽  
pp. 456 ◽  
Author(s):  
L. A. Hinds ◽  
C. H. Tyndale-Biscoe
Keyword(s):  
Corpus Luteum ◽  
Tammar Wallaby ◽  
Marked Contrast ◽  
Previous Conclusion ◽  
Macropus Eugenii ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Progesterone Synthesis ◽  
Rate Limiting

The corpus luteum (CL) of the tammar wallaby is inhibited by prolactin during lactation and seasonal quiescence. In seasonal quiescence a daily transient pulse of prolactin (PRL) of less than 2 h duration is sufficient to maintain inhibition. We investigated whether the same inhibition applies in lactation and, if so, how. Our results show that inhibition of the CL during lactation is maintained by a transient pulse of prolactin once a day. They also show that the minimum time without a PRL pulse for the CL to escape inhibition is more than 48 h and less than 72 h. Nevertheless, some animals had a longer refractory period than 72 h, which was reflected in a longer interval to the progesterone peak and birth. These results support the previous conclusion that PRL exercises its effect on a rate-limiting step in progesterone synthesis and secretion rate from the CL, which precedes any increase in its mass. Therefore, we conclude that the role of PRL is to act as a luteostatic agent, an effect that is in marked contrast to its luteotrophic effect in many eutherian species, including rodents.

scholarly journals Role of Thr66in Porcine NADH-cytochromeb5Reductase in Catalysis and Control of the Rate-limiting Step in Electron Transfer

2002 ◽  
Vol 278 (6) ◽  
pp. 3580-3589 ◽  
Author(s):  
Shigenobu Kimura ◽  
Masanori Kawamura ◽  
Takashi Iyanagi
Keyword(s):  
Electron Transfer ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
And Control ◽  
Rate Limiting

scholarly journals Production and Peripheral Roles of 5-HTP, a Precursor of Serotonin

2009 ◽  
Vol 2 ◽  
pp. IJTR.S1022 ◽  
Author(s):  
Kazuhiro Nakamura ◽  
Hiroyuki Hasegawa
Keyword(s):  
Tryptophan Hydroxylase ◽  
Systemic Treatment ◽  
Biological Significance ◽  
Review Article ◽  
Enzyme Reactions ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting ◽  
Shed Light

Serotonin (5-hydroxytryptamine [5-HT]) has been implicated in a variety of physiological and pathological functions. Multiple steps of enzyme reactions enable biosynthesis of 5-HT. The first and rate-limiting step of the reaction is the synthesis of 5-hydroxy- L-tryptophan (5-HTP) from L-tryptophan. This step is dictated by an enzyme, tryptophan hydroxylase (TPH). TPH requires 6R- L-erythro-5,6,7,8-tetrahydrobiopterin (BH4) as a co-substrate of TPH. 5-HTP has been simply regarded as a precursor of 5-HT and it is believed that the biological significance of 5-HTP is essentially ascribed to the production of 5-HT. However, recent works shed light on the specific functions of 5-HTP in the periphery. In this review article, we focus on the specific roles of exogenous 5-HTP as well as the endogenous 5-HTP in the gut epithelial cells. Since systemic treatment with 5-HTP is applied to patients with lower 5-HT levels, the studies on the specific role of 5-HTP might create an opportunity to explore the effects of exogenously-applied 5-HTP in the gut in man.

4-Nitro-L-histidine as a substrate for histidine ammonia-lyase: The role of β-hydrogen acidity in the rate-limiting step

1979 ◽  
Vol 87 (1) ◽  
pp. 343-348 ◽  
Author(s):  
Claude B. Klee ◽  
Kenneth L. Kirk ◽  
Louis A. Cohen
Keyword(s):  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

scholarly journals Feasibility of Solar Updraft Towers as Photocatalytic Reactors for Removal of Atmospheric Methane–The Role of Catalysts and Rate Limiting Steps

2021 ◽  
Vol 9 ◽  
Author(s):  
Yanfang Huang ◽  
Yimin Shao ◽  
Yang Bai ◽  
Qingchun Yuan ◽  
Tingzhen Ming ◽  
...  
Keyword(s):  
Greenhouse Gas ◽  
Removal Rate ◽  
Atmospheric Methane ◽  
Planetary Scale ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Gas Removal ◽  
Photocatalytic Reactors ◽  
Rate Limiting

Due to the alarming speed of global warming, greenhouse gas removal from atmosphere will be absolutely necessary in the coming decades. Methane is the second most harmful greenhouse gas in the atmosphere. There is an emerging technology proposed to incorporating photocatalysis with solar updraft Towers (SUT) to remove methane from the air at a planetary scale. In this study, we present a deep analysis by calculating the potential of methane removal in relation to the dimensions and configuration of SUT using different photocatalysts. The analysis shows that the methane removal rate increases with the SUT dimensions and can be enhanced by changing the configuration design. More importantly, the low methane removal rate on conventional TiO2 photocatalyst can be significantly improved to, for example, 42.5% on a more effective Ag-doped ZnO photocatalyst in a 200 MW SUT while the photocatalytic reaction is the rate limiting step. The factors that may further affect the removal of methane, such as more efficient photocatalysts, night operation and reaction zone are discussed as possible solutions to further improve the system.

scholarly journals Tryptophan 2,3-Dioxygenase Expression Identified in Murine Decidual Stromal Cells Is Not Essential for Feto-Maternal Tolerance

2020 ◽  
Vol 11 ◽  
Author(s):  
Delia Hoffmann ◽  
Tereza Dvorakova ◽  
Florence Schramme ◽  
Vincent Stroobant ◽  
Benoit J. Van den Eynde
Keyword(s):  
Stromal Cells ◽  
Kynurenine Pathway ◽  
Immune Rejection ◽  
Cell Type ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Tryptophan Catabolism ◽  
Maternal Tolerance ◽  
Rate Limiting

Indoleamine 2,3-dioxygenase 1 (IDO1) and tryptophan 2,3-dioxygenase (TDO) catalyze the rate-limiting step of tryptophan catabolism along the kynurenine pathway, which has important immuno suppressive properties, particularly in tumor cells and dendritic cells. The prominent expression of IDO1 in the placenta also suggested a role in preventing immune rejection of fetal tissues, and pharmacological inhibition of IDO1 induced abortion of allogeneic fetuses in mice. However, this was later challenged by the lack of rejection of allogeneic fetuses in IDO1-KO mice, suggesting that other mechanisms may compensate for IDO1 deficiency. Here we investigated whether TDO could contribute to feto-maternal tolerance and compensate for IDO1 deficiency in IDO1-KO mice. Expression of TDO mRNA was previously detected in placental tissues. We developed a new chimeric rabbit anti-TDO antibody to confirm TDO expression at the protein level and identify the positive cell type by immunohistochemistry in murine placenta. We observed massive TDO expression in decidual stromal cells, starting at day E3.5, peaking at day E6.5 then declining rapidly while remaining detectable until gestation end. IDO1 was also induced in decidual stromal cells, but only at a later stage of gestation when TDO expression declined. To determine whether TDO contributed to feto-maternal tolerance, we mated TDO-KO and double IDO1-TDO-KO females with allogeneic males. However, we did not observe reduced fertility. These results suggest that, despite its expression in decidual stromal cells, TDO is not a dominant mechanism of feto-maternal tolerance able to compensate for the absence of IDO1. Redundant additional mechanisms of immunosuppression likely take over in these KO mice. The massive expression of TDO during decidualization might suggest a role of TDO in angiogenesis or vessel tonicity, as previously described for IDO1.

THE UPTAKE OF GLUCOSE INTO CELLS AND THE ROLE OF INSULIN IN GLUCOSE TRANSPORT

1964 ◽  
Vol 42 (6) ◽  
pp. 933-944 ◽  
Author(s):  
Margaret J. Henderson
Keyword(s):  
Cell Membrane ◽  
Glucose Uptake ◽  
Glucose Transport ◽  
Glucose Levels ◽  
Insulin Transport ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Extracellular Glucose ◽  
Rate Limiting

This presentation has been restricted to the role of insulin in glucose transport in muscle cells and deals mainly with experiments using the perfused rat heart. The several possible means for glucose transfer into cells, diffusion, pores, pinocytosis, carriers, and dimerization, have been discussed; and arguments in favor of the carrier theory, namely, specificity, kinetics, inhibition, competition, and counterflow, have been elaborated. Glucose uptake has been considered to consist of three sequential steps: (1) passage of glucose from within the capillary to the cell surface, (2) transport across the cell membrane, and (3) metabolism of glucose within the cell. The first is considered to take place by diffusion and not to be significantly limiting under normal conditions, nor to be influenced by insulin. Transport across the cell membrane is thought to be mainly under the control of insulin and is the major rate-limiting step in glucose uptake when the extracellular glucose levels are in the normal range. Metabolism of glucose within the cell is the major rate-limiting step in glucose uptake when intracellular glucose concentration is so high that its phosphorylation is near saturation.

scholarly journals Role of Asp104 in the SHV β-Lactamase

2006 ◽  
Vol 50 (12) ◽  
pp. 4124-4131 ◽  
Author(s):  
Christopher R. Bethel ◽  
Andrea M. Hujer ◽  
Kristine M. Hujer ◽  
Jodi M. Thomson ◽  
Mark W. Ruszczycky ◽  
...  
Keyword(s):  
Amino Acid ◽  
Catalytic Efficiency ◽  
Saturation Mutagenesis ◽  
Amino Acid Residues ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Threefold Increase ◽  
Rate Limiting ◽  
Hydrolysis Of

ABSTRACT Among the TEM-type extended-spectrum β-lactamases (ESBLs), an amino acid change at Ambler position 104 (Glu to Lys) results in increased resistance to ceftazidime and cefotaxime when found with other substitutions (e.g., Gly238Ser and Arg164Ser). To examine the role of Asp104 in SHV β-lactamases, site saturation mutagenesis was performed. Our goal was to investigate the properties of amino acid residues at this position that affect resistance to penicillins and oxyimino-cephalosporins. Unexpectedly, 58% of amino acid variants at position 104 in SHV expressed in Escherichia coli DH10B resulted in β-lactamases with lowered resistance to ampicillin. In contrast, increased resistance to cefotaxime was demonstrated only for the Asp104Arg and Asp104Lys β-lactamases. When all 19 substitutions were introduced into the SHV-2 (Gly238Ser) ESBL, the most significant increases in cefotaxime and ceftazidime resistance were noted for both the doubly substituted Asp104Lys Gly238Ser and the doubly substituted Asp104Arg Gly238Ser β-lactamases. Correspondingly, the overall catalytic efficiency (k cat/Km ) of hydrolysis for cefotaxime was increased from 0.60 ± 0.07 μM−1 s−1 (mean ± standard deviation) for Gly238Ser to 1.70 ± 0.01 μM−1 s−1 for the Asp104Lys and Gly238Ser β-lactamase (threefold increase). We also showed that (i) k 3 was the rate-limiting step for the hydrolysis of cefotaxime by Asp104Lys, (ii) the Km for cefotaxime of the doubly substituted Asp104Lys Gly238Ser variant approached that of the Gly238Ser β-lactamase as pH increased, and (iii) Lys at position 104 functions in an energetically additive manner with the Gly238Ser substitution to enhance catalysis of cephalothin. Based on this analysis, we propose that the amino acid at Ambler position 104 in SHV-1 β-lactamase plays a major role in substrate binding and recognition of oxyimino-cephalosporins and influences the interactions of Tyr105 with penicillins.

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