21 Malfunction in Glycolysis

Dr.Vikram Raval

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Malfunction in Glycolysis

 

Objectives

 

1.     To understand the concept of malfunction.

2.     To understand the biochemistry during the malfunction of glycolysis

3.     To understand diseases associated with the malfunction of glycolysis.

 

 

 Introduction

  • Malfunction means a failure to function normally
  • Word Glycolysis has been actually derived from two terms from Greek language “glyk” meaning sweet and “lysis” meaning splitting or solubilisation
  • One of the meaning of Glycolysis can essentially be glycol (sugar) + lysis (breakdown) i.e breakdown of sugar. In higher organisms principal sugar present is glucose this it can be called breakdown of glucose molecule
  • It is also one among the most ancient metabolic pathways known to human race
  • Malfunction of glycolysis leads to Inborn Metabolic Disorders. It is also called Inborn Errors of Metabolism
  • In born errors of metabolism are a set of genetic diseases occurs due to malfunctioning of a specific metabolic pathway
  • Metabolic pathways consist of a number of processes. It involves sequence of chemical reactions. This reaction occurs in human body on products of dietary or endogenous origin with the aim of make it available or avoids their accumulation.
  • Consequences of the Malfunction/block of the metabolic pathway:

    Accumulation of precursors found before the biochemical fault which leads to toxic effects;

Deficiency of the final products /metabolite of the metabolic pathway , It lead to a fault in energy production;

Activation of alternative pathways (if present/available) with creation of potentially toxic metabolites usually not found in organism.

 

 

  • Coexistence of above described mechanism is possible. Generally a metabolic disease involves more organs. It also shows systematic symptoms.
  • Glycolysis is a process that is constituted by sequential biochemical reactions through which a single molecule of glucose [6C] can be metabolized completely giving 2 molecules of Pyruvate [3C] (pyruvic acid) and an overall yield of energy equivalent to 2 ATP
  • Primarily cytosol or a more common term cytoplasm is the place within the cell where chiefly all the reactions of glycolysis occur
  • Glycolysis is a pathway that is anaerobic organisms by which mode of respiratory mechanism common to both aerobic as well as they acquire preliminary energy as a
  • Glycolysis, is a process which as a whole does not require a single oxygen molecule in glucose metabolism and hence technically a process which is anaerobic in nature. But similar reactions do occur in aerobic organisms though oxygen is present in cellular environment but is not involved in glucose breakdown and does not affect it
  • The end product of glycolysis is a three carbon intermediate Pyruvate [3C] which can further be metabolised in two ways

 

     1. Anaerobic                             2.Aerobic

 

  • Towards the end of nineteenth century an absolute map of glycolysis was expounded. Gustav G. Embden a German chemist, Otto F. Meyerhof, a German physician and biochemist and Jakub K. Pernas, a Russian biochemist, were the pioneers of this work.
  • Embden studied the metabolism in liver and basics behind diabetes. Embden studied thoroughly carbohydrate metabolism, muscle contraction and later of conversion of glucose to lactic acid. He also linked the key step involved in this metabolism
  • Meyerhof correlated his work on muscle contraction and muscle metabolism with the former studies
  • While Jakub Parnas mainly focused on carbohydrate metabolism in muscle tissues. The entire theoretical analysis of glycolysis had been proposed by Parnas giving a perfect shape to metabolic process and breakdown of glycose
  • Hence the pathway is collectively referred to as the Embden-Meyerhof-Pernas pathway owing to their contributions and efforts made towards better understanding of the mechanism
  • Carl A. Neuberg, a German biochemist made a noteworthy contribution by studying alcoholic fermentations of glucose in yeast and other anaerobes
  • Otto H. Warburg, a German physiologist and biochemist did a keynote discovery of various enzymes involved in fermentative processes
  • Gerty T. Cori and her husband Carl F. Cori both were Czech biochemists and did a notable contribution in studying glycogen breakdown in muscle tissues and formation of lactic acid and vice-versa the reverse mechanism of formation of glycogen popularly called The Cori cycle
  • M.Doudoroff born Russian but migrated to America, a microbiologist by profession and his student Nathan Entner worked on alternative pathways by which reactions similar to glycolysis are performed in different prokaryotes specially archaea. To commemorate their contributions the alternative pathway is popularly called Entner-Doudoroff pathway
  • Metabolic disorders arise because of malfunctioning of specific enzymes (structural deformities of protein or its cofactor) or defect in cellular transportation

 

   For your information (FYI):

 

Entner-Doudoroff pathway considerably varies from a classic glycolytic pathway. Here two different enzymes viz. 6-phosphogluconate dehydratase and 2-keto-3-deoxyphosphogluconate aldolase are engaged for the catabolism of pyruvate. As a matter of fact the energy efficiency of ED pathway is only 50% to that of EMP pathway. In ED pathway there is formation of a singly ATP molecule while for each glucose molecule 2ATP are formed in EMP pathway

 

   Overview of Glycolysis cycle

  • Glycolytic pathway comprise of 10 different reactions that lead to two moles of pyruvic acid from one mole of glucose as an end product. All of the reactions are catalysed by specific enzymes and enlisted below
  • Glucose to Glucose-6-phosphate is a phosphorylation reaction that draws energy from ATP and is an irreversible reaction catalysed by hexokinase (glucokinase)

 

 

For your information (FYI):

 

Hexokinase is the enzyme that initiates glycolysis in muscles, brain and other vital tissues while glucokinase is the enzyme that does similar reactions in liver and pancreas.

  • Glucose-6-phosphate to Fructose-6-phosphate a reversible isomerisation reaction catalysed by glucose-6-phosphate isomerase enzyme (also called phosphoglucomutase)
  • Fructose-6-phosphate to Fructose-1-6-bisphosphate is another irreversible reaction of this pathway and is catalysed by phosphofructokinase enzyme utilizing energy from ATP
  • Fructose-1-6-bisphosphate to 2 molecules of glycerladehyde-3-phosphate. Fructose-1,6-bisphosphate actually splits into 2 3-carbon moieties, an aldehyde and a ketone: glyceraldehyde 3-phosphate (GAP) and di-hyroxy-acetone-phosphate (DHAP). The reaction is catalysed by fructose-bis-phosphate aldolase enzyme

 

For your information (FYI):

 

In glycolytic pathway dihydroxy-acetone-phosphate (DHAP) and Glyceraldehyde -3-phoshpate (GAP) [also called Phosphoglyceraldehyde (PGAL]) are isomers and are easily interconvertible. A reaction catalysed by triose-phosphate isomerase. Glyceraldehyde -3-phoshpate acts as a substrate for glycolytic reactions and hence the entire keto-product DHAP is converted to PGAL (GAP). Hence we now have 2 molecules of GAP from each molecule of glucose

  • 2 molecules of glycerladehyde-3-phosphate to 1-3-bisphosphoglycerate a dehydrogenation reaction catalysed by glyceraldehydes-3-phosphate dehydrogenase. Here in this reaction, NAD+ is reduced to NADH + H+ from NAD. Additionally above oxidation reaction is coupled with a phosphorylation reaction that yields 1-3-bisphosphoglycerate
  • 1-3-bisphosphoglycerate to 3-phosphoglycerate is an exergonic reaction catalysed by phosphoglycerate kinase high energy bond in 1-3-bisphosphoglycerate is hydrolyzed to a carboxylic acid and the energy liberated in that is used conveniently for the formation of energy rich phosphate bond of ATP from ADP
  • 3-phosphoglycerate to 2-phosphoglycerate reaction where phosphate group shifts from 3rd position to the 2nd position. The reaction is an isomerisation reactions and is catalysed by phosphoglycerate mutase
  • 2-phosphoglycerate to phospho-enol-pyruvate a dehydration reaction catalysed by an enolase (phosphor-puryvate hydratase)
  • Phospho-enol-pyruvate to pyruvate, an irreversible reaction is catalysed by transferase activity followed by dephosphorylation. The enzyme involved is Pyruvate kinase. The enolphosphate intermediate has a high energy phosphate bond which when hydrolyzed is converted to enolic form of Pyruvate along with formation of ATP. Enol pyruvate quickly changes to keto pyruvate which is far more stable.

 

Malfunction in glycolysis

  • Glycolysis is a very important process for every organism. Mutation alters the gene involved in glycolysis. It alters the chain of reaction involved in the process. Malfunctioning of glycolysis leads to diseased condition.
  • Hexokinase malfunction

 

Hexokinase is present in most of the tissues. It has broad specificity. i.e. it acts on many sugars. It has high affinity for glucose i.e. low Km. It converts glucose in to G6P during the low blood glucose levels. It has low Vmax so it cannot phosphorylate high glucose quantities. It has low capacity for working on glucose. It is inhibited by G6P.

 

Hexokinase deficiency: Deficiency of hexokinase results in to the autosomal recessive diseases. It causes haemolytic anaemia. In hexokinase deficiency the 2, 3 DPG level is decreased. This will increase the affinity of haemoglobin for oxygen. This results in to the difficulty in releasing oxygen to the tissues. Finally it causes the tissue anoxia. ATP formation will stop and causes haemolytic anaemia.

 

  • PFK malfunction

          Fructose-6- phosphate is converted to fructose-1, 6- bisphosphate by phosphofructokinase. Low energy i.e. high content of AMP will activate the phosphofructokinase. ATP inhibits the phosphofructokinase.

 

 

PFK deficiency: Deficiency of PFK results in to the genetic disorder. It results in to the TYPE VII Glycogen storage diseases. It is observed due to mutation in the gene of M subunit of the Phosphofructokinase enzyme. PFKM. This gene helps in the synthesis of phosphofructokinase. PFK phosphorylates fructose-6-phosphate preceding to its cleavage into glyceraldehyde-3-phosphate which enters the energy generation phase of glycolysis

 

 

Pyruvate kinase malfunction

   Pyruvate is the end product of glycolysis. Two pyruvic acid molecules are formed from the two molecules of phosphoenol pyruvate. This reaction is catalysed by pyruvate kinase.

 

Pyruvate kinase deficiency: Red blood cells do not have mitochondria. They are dependent on the glycolysis for their energy requirement. So pyruvate kinase deficiency causes low RBC glycolysis. Low ATP affects K+/Na+-ATPase pump, and leads to membrane damage, lysis and hemolytic anemia. It leads to abnormal accumulation of intermediates of glycolysis. In pyruvate kinase deficiency the 2, 3 DPG level is increased. This will decrease the affinity of haemoglobin for oxygen. Finally it causes the tissue anoxia. ATP formation will stop and causes haemolytic anaemia.

    Aldolase A malfunction

 

It is a genetic disorder. It is an autosomal recessive disorder. It results due to deficiency of Aldolase A enzyme.It is caused due to homozygous mutation in the ALDOA gene. ALDOA gene encodes fructose-1,6-bisphosphate Aldolase A. Aldolase A catalyses the aldol reaction. This reaction is reversible. It act on the fructose 1,6-bisphosphate (F-1,6-BP) . Fructose 1,6-bisphosphate is split to into glyceraldehydes 3-phosphate and dihydroxyacetone phosphate (DHAP).

 

 

 

GLYCOGEN STORAGE DISEASE ASSOCIATED WITH MALFUNCTIOIN INGLYCOLYSIS

 

Type VII Tarui’s disease (Deficiency of phosphofructokinase in muscle and erythrocytes)

 

It is a genetic disorder

 

It is directly related to impairment in the glycolysis. In this disease patient is unable to breakdown glycogen in muscle cells.It result in to the interference in the functioning of muscle cells.

  Four types of GSD Type VII is observed

 

The classical form is the most common form. Its symptoms observed in childhood. It is characterised by muscle pain and cramps after moderate exercise. Exercise results in to the breakdown of muscles. It releases the protein called myoglobin. It results in to the myoglobinuria. If untreated, myoglobinuria can harm the kidneys and lead to kidney failure.

 

 

 

Glycogen Storage Disease Type XII (Aldolase A Deficiency, Glycogenosis Type 12, red cell Aldolase deficiency)

 

 

It is a genetic disorder

 

It is an autosomal recessive disorder

 

It results due to deficiency of Aldolase A enzyme.

 

It is caused due to homozygous mutation in the ALDOA gene. ALDOA gene encodes fructose-1,6-bisphosphate Aldolase A

  • Aldolase A catalyses the aldol reaction. This reaction is reversible. It act on the fructose 1,6-bisphosphate (F-1,6-BP) . Fructose 1,6-bisphosphate is split to into glyceraldehydes 3-phosphate and dihydroxyacetone phosphate (DHAP).

    This reaction observed in the glycolysis.

 

Symptoms: Exercise intolerance and cramps

 

Aldolase exist in three isoforms i.e. Aldolase A , Aldolase B and Aldolase C.

 

Aldolase A is predominately found in the skeletal muscles and erythrocytes.

 

Kishi et al. (1987) reported the mutation in the ALDOA gene (asp128-to-gly) while Kreuder et al. (1996) identified a homozygous mutation in the ALDOA gene ( glutamic acid to lysine )

 

 

    For your information (FYI):

 

Warburg effect and anticancer treatment: Metabolic alteration is observed in malignant cells. Cancerous cells shows high rate of glycolysis. Cancerous cells utilize this metabolic pathway for synthesis of ATP. It acts as a major source of their energy supply. This phenomenon is known as the Warburg effect. Biochemical and molecular studies propose numerous potential means by which this metabolic alteration may develop during progress of cancer. These mechanisms include mitochondrial defects and malfunction in glycolysis. Cancerous cell have high dependency on glycolytic pathway for generation of ATP. This phenomenon provides a metabolic basis for the development of therapeutic strategies to develop an anticancer treatment. Inhibitors of glycolysis particularly against cancerous cells with mitochondrial defects may be develop by studying the malfunctions in glycolysis.

 

you can view video on Malfunction in Glycolysis

 

References

  • John Hicks, Eric Wartchow, James Barrish , Shen-Hua, Zhu Gary Mierau. Glycogen Storage Diseases: A Brief Review and Update on Clinical Features, Genetic Abnormalities, Pathologic Features and Treatment. ULTRASTRUCTURAL PATHOLOGY. (2011) DOI: 10.3109/01913123.2011.601404.
  • Bayraktar Y. Glycogen storage diseases: new perspectives. World J Gastroenterol 207;13(18):2541-53
  • Wolfsdorf JI, Weinstein DA. Glycogen storage diseases. Reviews Endocrinol Metab Disorders 2003;4:95-102.

 

Web site

  • http://www.medchrome.com/basic-science/biochemistry/glycogen-metabolism-and- glycogenstorage
  • https://www.uic.edu/classes/phar/phar332/Clinical_Cases/carbometabcases/glycog enmetab/
  • http://themedicalbiochemistrypage.org/glycogen.php
  • https://en.wikibooks.org/wiki/Principles_of_Biochemistry/Gluconeogenesis_and_Gly cogenesis

 

Books

  • Nyhan, William L., Pinar, T. Ozand, Atlas of Metabolic Diseases, Chapman & Hall Medical, 1998.
  • Harper’sIllustrated Biochemistry by Robert K.. Murray, Daryl K. Granner, Peter A. Mayes, 26th Edition (2003)
  • Lehninger’S Principle of Biochemistry David L. Nelson and Michael M. Cox,5th Edition (2008)
  • Textbook of Biochemistry, 4th Edition Donald Voet, Judith G. Voet (2011)
  • Fernandes J, Smit GPA (2000) The glycogen storage diseases. In: Fernandes J, Saudubray J-M, Berghe G van den (eds) Inborn errors of metabolism, 3rd edn. Springer,Berlin Heidelberg New York, pp 86–101