scholarly journals Developmental changes in the activity of phosphatidylethanolamine N-methyltransferases in rat brain

1985 ◽  
Vol 232 (2) ◽  
pp. 505-511 ◽  
Author(s):  
J K Blusztajn ◽  
S H Zeisel ◽  
R J Wurtman
Keyword(s):  
Rat Brain ◽  
Neonatal Period ◽  
Enzyme System ◽  
Adult Brain ◽  
Developmental Changes ◽  
Hill Coefficient ◽  
Neonatal Brain ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

The activity of phosphatidylethanolamine N-methyltransferase (PeMT), an enzymic system that catalyses the synthesis of phosphatidylcholine (PtdCho) via sequential methylation of phosphatidylethanolamine (PtdEtn) using S-adenosylmethionine (AdoMet) as a methyl donor, was examined in brain homogenates from rats of various ages. The data thus obtained were consistent with the existence of two distinct enzyme activities within this enzyme system, i.e. one catalysing the methylation of PtdEtn [to form phosphatidyl-N-monomethylethanolamine (PtdMeEtn)], and the other catalysing the methylations of PtdMeEtn and phosphatidyl-NN-dimethylethanolamine (PtdMe2Etn) (to form PtdMe2Etn and PtdCho, respectively). PeMT (PtdEtn-methylating) activity per g of brain was 4-fold higher in neonatal than in adult brains. The enzyme activity in adult brains exhibited Michaelis-Menten kinetics for AdoMet, and its affinity for AdoMet was high (apparent Km 1.6 microM). In neonatal brain the relationships between AdoMet concentrations and PtdMeEtn formation were more complex: a sigmoidal component (with a Hill coefficient of 2.7), requiring 90 microM-AdoMet for half-saturation predominated over the high-affinity component (similar to that of the adult brain). PeMT (PtdMe2Etn-methylating) activity per g of brain increased 2-fold between the 5th and the 20th postnatal days and remained constant thereafter; it was higher than that of PeMT (PtdEtn-methylating) activity at all ages studied, and its affinity for AdoMet was low (apparent Km 99 microM). No sexual dimorphism in brain PeMT activity was observed at any age. We conclude that PeMT (PtdEtn-methylating) catalyses the rate-limiting step in PtdCho synthesis in rat brain, and that PtdCho formation via this pathway may be greatest during the neonatal period.

scholarly journals The amine oxidases of human placenta and pregnancy plasma

1974 ◽  
Vol 139 (1) ◽  
pp. 169-181 ◽  
Author(s):  
William G. Bardsley ◽  
M. James C. Crabbe ◽  
Ian V. Scott
Keyword(s):  
Diamine Oxidase ◽  
Amine Oxidase ◽  
Enzyme System ◽  
Placental Tissue ◽  
Amine Oxidases ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Ping Pong ◽  
Normal Human ◽  
Rate Limiting

1. The purification of monoamine oxidase and diamine oxidase from normal human term placental tissue is described. 2. The properties of these enzymes are reported and compared with the properties of unpurified human pregnancy plasma. 3. This comparison shows that the amine oxidase of pregnancy plasma has properties corresponding to purified placental diamine oxidase, suggesting a placental origin for the plasma enzyme system. 4. Detailed kinetic study of the purified placental diamine oxidase suggests that it has a Ping Pong sequence, a mechanism of action and rate-limiting step similar to the diamine oxidase of pig kidney. 5. It is suggested that the enzyme system is important in protecting the foeto-placental unit from excesses of biogenic amines.

scholarly journals Activation of liver succinate dehydrogenase in rats exposed to hypobaric conditions

1969 ◽  
Vol 115 (1) ◽  
pp. 77-83 ◽  
Author(s):  
H. N. Aithal ◽  
T. Ramasarma
Keyword(s):  
Succinate Dehydrogenase ◽  
Enzyme System ◽  
Freezing And Thawing ◽  
Isolated Mitochondria ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Activated State ◽  
Sucrose Medium ◽  
Rate Limiting ◽  
State Of Activity

1. On brief exposure of rats to hypobaric conditions, the activity of hepatic mitochondrial succinate dehydrogenase was raised from the basal state to a ‘partially activated state’. This was further raised to ‘fully activated state’ by preincubation of mitochondria with succinate, as was the activity in mitochondria from normal rats. 2. On washing mitochondria with the homogenizing sucrose medium the activity excess obtained on preincubation with succinate was lost in mitochondria from both normal and treated rats. 3. The enzyme in the ‘partially activated state’ from animals exposed to hypobaric conditions was stable to the washing procedure but was labilized and reverted to a low basal state of activity on freezing and thawing of the isolated mitochondria. 4. The results suggest that activation of succinate dehydrogenase under hypobaric conditions represents a conformational change leading to a stable, partially activated, form of the enzyme system: this is the first evidence of physiological modulation of this rate-limiting step in the control of the rate of oxidation of succinate.

Ornithine Decarboxylase Activity in Cultured Endothelial Cells Stimulated by Serum, Thrombin and Serotonin

1978 ◽  
Vol 39 (02) ◽  
pp. 496-503 ◽  
Author(s):  
P A D’Amore ◽  
H B Hechtman ◽  
D Shepro
Keyword(s):  
Endothelial Cells ◽  
Ornithine Decarboxylase ◽  
Decarboxylase Activity ◽  
Aortic Endothelial Cells ◽  
Ornithine Decarboxylase Activity ◽  
Rate Limiting Step ◽  
Bovine Aortic Endothelial Cells ◽  
Limiting Step ◽  
Rate Limiting ◽  
Serum Serotonin

SummaryOrnithine decarboxylase (ODC) activity, the rate-limiting step in the synthesis of polyamines, can be demonstrated in cultured, bovine, aortic endothelial cells (EC). Serum, serotonin and thrombin produce a rise in ODC activity. The serotonin-induced ODC activity is significantly blocked by imipramine (10-5 M) or Lilly 11 0140 (10-6M). Preincubation of EC with these blockers together almost completely depresses the 5-HT-stimulated ODC activity. These observations suggest a manner by which platelets may maintain EC structural and metabolic soundness.

Dynamics of hepatic and peripheral insulin effects suggest common rate-limiting step in vivo

Diabetes ◽  
1993 ◽  
Vol 42 (2) ◽  
pp. 296-306 ◽  
Author(s):  
D. C. Bradley ◽  
R. A. Poulin ◽  
R. N. Bergman
Keyword(s):  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

Kinetics of cyclization of S-ethoxycarbonylmethylisothiouronium chloride to 2-imino-4-thiazolidone

1979 ◽  
Vol 44 (3) ◽  
pp. 912-917 ◽  
Author(s):  
Vladimír Macháček ◽  
Said A. El-bahai ◽  
Vojeslav Štěrba
Keyword(s):  
Hydrochloric Acid ◽  
Dilute Hydrochloric Acid ◽  
Base Catalysis ◽  
General Base ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Kinetics Of Formation ◽  
Acid Catalyzed ◽  
Rate Limiting ◽  
Kinetics Of

Kinetics of formation of 2-imino-4-thiazolidone from S-ethoxycarbonylmethylisothiouronium chloride has been studied in aqueous buffers and dilute hydrochloric acid. The reaction is subject to general base catalysis, the β value being 0.65. Its rate limiting step consists in acid-catalyzed splitting off of ethoxide ion from dipolar tetrahedral intermediate. At pH < 2 formation of this intermediate becomes rate-limiting; rate constant of its formation is 2 . 104 s-1.

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