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Related Concept Videos

Urea Cycle01:23

Urea Cycle

The urea cycle describes how liver cells convert ammonia to urea. Ammonia is a toxic waste product of protein catabolism. Land animals must convert ammonia into the less toxic urea which can be safely eliminated by the kidneys through urine. Marine animals excrete ammonia directly, and the surrounding water dilutes the ammonia to safe levels.
The Citric Acid Cycle02:36

The Citric Acid Cycle

The citric acid cycle, also known as the Krebs cycle or TCA cycle, consists of several energy-generating reactions that yield one ATP molecule, three NADH molecules, one FADH2 molecule, and two CO2 molecules.
The Citric Acid Cycle: Output01:28

The Citric Acid Cycle: Output

The citric acid cycle is termed an amphibolic pathway as it operates both anabolically and catabolically. The cyclic reactions balance the flux of the substrates to provide an optimal concentration of NADH and ATP to the cell.
Regulation of Citric Acid Cycle
The citric acid cycle is regulated in several ways, including feedback inhibition, regulation of enzyme activities, and associated anaplerotic or cataplerotic pathways.
The primary substrate of the TCA cycle—acetyl CoA—is produced by the...
The Citric Acid Cycle: Overview01:37

The Citric Acid Cycle: Overview

In aerobic organisms, the citric acid cycle is the second stage of cellular respiration wherein molecules derived from the breakdown of carbohydrates, proteins, and fats are oxidized into carbon dioxide and energy. This process is also known as the tricarboxylic acid (TCA) cycle as the first product of the cycle, citric acid, contains three carboxyl groups in its structure. Alternatively, this cycle is also referred to as the Krebs cycle, in honor of its discoverer Sir Hans Krebs.
The citric...
Drug Dosing in Renal Diseases: Measurement of Serum Creatinine Concentration and Clearance01:25

Drug Dosing in Renal Diseases: Measurement of Serum Creatinine Concentration and Clearance

In healthy individuals, serum creatinine levels remain stable due to a balance between its constant production—primarily from muscle metabolism—and renal excretion. Creatinine is freely filtered by the glomeruli, making it a valuable marker for estimating renal function. When the glomerular filtration rate (GFR) decreases, the kidneys can only eliminate less creatinine, causing serum levels to rise.Serum creatinine concentration is widely used to estimate creatinine clearance (Clcr), a...
Comparative Excretory Systems02:24

Comparative Excretory Systems

Animals have evolved different strategies for excretion, the removal of waste from the body. Most waste must be dissolved in water to be excreted, so an animal’s excretory strategy directly affects its water balance.

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Related Experiment Video

Updated: Jun 14, 2026

Phosphorus-31 Magnetic Resonance Spectroscopy: A Tool for Measuring In Vivo Mitochondrial Oxidative Phosphorylation Capacity in Human Skeletal Muscle
09:40

Phosphorus-31 Magnetic Resonance Spectroscopy: A Tool for Measuring In Vivo Mitochondrial Oxidative Phosphorylation Capacity in Human Skeletal Muscle

Published on: January 19, 2017

Creatine metabolism and the urea cycle.

John T Brosnan1, Margaret E Brosnan

  • 1Department of Biochemistry, Memorial University of Newfoundland, St. John's, NL, Canada. jbrosnan@mun.ca

Molecular Genetics and Metabolism
|March 23, 2010
PubMed
Summary

Creatine is essential and synthesized from arginine. Urea cycle disorders disrupt creatine metabolism, potentially impacting neurological symptoms due to altered arginine levels and creatine synthesis rates.

Area of Science:

  • Biochemistry
  • Metabolic Disorders
  • Neuroscience

Background:

  • Creatine and creatine phosphate are irreversibly converted to creatinine, necessitating continuous replacement through diet and de novo synthesis.
  • Dietary creatine, primarily from animal products, supplies about half the body's needs, with synthesis providing the remainder.
  • Creatine synthesis is a significant metabolic pathway, representing over 20% of dietary arginine utilization.

Purpose of the Study:

  • To explore the implications of creatine metabolism alterations in patients with urea cycle disorders.
  • To investigate the relationship between arginine levels, creatine synthesis, and potential neurotoxicity in these patients.

Main Methods:

  • The study is a review of existing literature and metabolic pathways.

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Analysis of Human Natural Killer Cell Metabolism

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Last Updated: Jun 14, 2026

Phosphorus-31 Magnetic Resonance Spectroscopy: A Tool for Measuring In Vivo Mitochondrial Oxidative Phosphorylation Capacity in Human Skeletal Muscle
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Phosphorus-31 Magnetic Resonance Spectroscopy: A Tool for Measuring In Vivo Mitochondrial Oxidative Phosphorylation Capacity in Human Skeletal Muscle

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Evaluation of Amino Acid Consumption in Cultured Bone Cells and Isolated Bone Shafts

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  • Analysis of the impact of altered arginine levels on creatine synthesis rates.
  • Examination of potential links between creatine metabolism and neurological symptoms in urea cycle disorders.

    • Main Results:

    • In arginase deficiency, elevated arginine may increase guanidinoacetate and creatine synthesis, potentially causing neurotoxic effects.
    • In other urea cycle disorders, decreased arginine levels can reduce creatine synthesis rates.
    • Low protein diets in these patients further limit dietary creatine intake, possibly lowering brain creatine levels and exacerbating neurological symptoms.

    Conclusions:

    • Patients with urea cycle disorders exhibit altered creatine metabolism.
    • The contribution of these metabolic changes to the neurological symptoms in urea cycle disorders remains an open question.
    • Further research is needed to elucidate the precise role of creatine metabolism in the pathophysiology of urea cycle disorders.