OXYGEN-BINDING PROTEINS: HEMOGLOBIN AND MYOGLOBIN

Normal hemoglobin is?

α2β2

Fetal hemoglobin is

α2γ2

Sickle cell disease (SCD) is

α2β s 2

Hemoglobin that is desaturated with oxygen is deoxyhemoglobin (T, tense form), which has a ______________ oxygen affinity and a _________ degree of freedom.

Low

Hemoglobin that is saturated with oxygen is oxyhemoglobin (R, relaxed form), which has a ____________ oxygen affinity and a _________ degree of freedom.

High

The O2-binding curve shifts (left/ right) with increase in CO2, acidosis (low pH), increase in 2,3- BPG, exercise, and temperature.

Right

True or False

A leftward shift in the oxygen saturation curve occurs in the presence of a decrease in CO2, alkalosis (high pH, low hydrogen ion concentration), and decrease in 2,3-BPG

True

Comparison of oxygen-binding curves for hemoglobin and myoglobin. The P50 is the Po2 at half saturation. What does p50 signify?

Having a lower P50 means having a greater affinity for oxygen.

Myoglobin is present in?

Heart and skeletal muscle and acts as an oxygen carrier and location for storage of oxygen.

Myoglobin can only bind to one oxygen molecule; therefore the binding curve is

binding curve is hyperbolic

Carbon monoxide (CO) binds to hemoglobin to form carboxyhemoglobin, which has a high affinity for CO and displaces O2. What happens to the curve in CO poisoning?

CO poisoning causes stabilization of the R state, a leftward shift in O2 saturation curve, and a saturation curve for hemoglobin that resembles the curve for myoglobin.

Myoglobin has a lower P50 than hemoglobin; therefore it has a greater affinity for O2. Thus O2 is bound to myoglobin in all cases except .

hypoxia

Hemoglobinopathies - Sickle cell characterization

• homozygous recessive genetic disorder that

• results from production of hemoglobin with an altered amino acid sequence,

• caused by a single point mutation in the β-globin gene.

• Mutation is a glutamate-to-valine mutation at position 6 in the β-globin chain.

Sickling is increased by anything that increases the proportion of HbS in the deoxygenated state such as

• decreased O2 tension,

• increased Pco2,

• decreased pH,

• dehydration,

• increased concentration of 2,3-BPG in erythrocytes.

An infant does not begin to show symptoms of the disease until sufficient HbF has been replaced by HbS so that sickling can occur. What is the treatment of sickle cell disease?

Hydroxyurea

Because it increases circulating levels of HbF, which decreases RBC sickling. Sickle cell disease is tested for at birth to allow prophylactic antibiotic therapy to begin soon after because these children are at risk for sepsis.

Hemoglobin C disease (HbC disease) results from production of hemoglobin with an altered amino acid sequence as a result of ?

Glutamate-to-lysine substitution at position 6 in the β-globin gene.

Homozygous patients have a mild, chronic hemolytic anemia.

Hemoglobin SC

occurs when some β-globin genes have the sickle cell mutation,

Thalassemias are caused by

decreased production of normal hemoglobin as a result of defective synthesis of either the α- or the β-globin chain

β-thalassemia the synthesis of Beta - globin chains is?

is decreased or absent, but the α-globin chain synthesis is normal.

e β-globin is not expressed until late in gestation, symptoms of β-thalassemia appear?

only after birth.

There are _______copies of the α-globin gene

Four

In Alpha - globin,

• If one copy of the α-globin is absent or defective, the person is a _______

• Two defective genes lead to_____________

• Three defective genes lead to _________

• If all four α-globin genes are defective it leads to _________

• Silent carrier

• α-thalassemia trait

• Hemoglobin H (HbH) disease.

• Hydrops fetalis and fetal death result because α-globin chains are required for the synthesis of HbF

Collagen is composed of a__________

Triple helix of three α-chains held together by hydrogen bonds

Collagen has a large amount of

proline and glycine

• Proline helps in the formation of the α-chain,

• Glycine is found in every third amino acid

• The sequence is –Gly–X–Y–, where X is often proline and Y is often hydroxyproline or hydroxylysine.

The biosynthesis of collagen

1. mRNA transcription in the nucleus of a fibroblast

2. mRNA is translated into pre-procollagen on the rough endoplasmic reticulum (RER), and these peptide chains are directed into the lumen of the RER and become pro-α-chains

3. Proline and lysine residues are next hydroxylated by prolyl hydroxylase and lysyl hydroxylase

4. Some hydroxylysine residues are glycosylated with glucose and galactose.

5. Pro-α-chains form procollagen, which has a central triple helix with N- and C-terminal propeptide extensions; these prevent premature assembly of collagen within the endoplasmic reticulum.

6. Procollagen is transported to the Golgi apparatus, where it is released into the extracellular space.

7. After release of procollagen, peptidases remove the terminal propeptides, forming tropocollagen.

8. Tropocollagen then spontaneously assembles into collagen fibrils.

   The collagen fibers are crosslinked by lysyl oxidase, which oxidatively deaminates lysyl and hydroxylysyl residues in collagen, forming covalent cross-linked, mature collagen fibers

In collagen synthesis, The hydroxylation reaction requires both

Oxygen and the reducing agent vitamin C (ascorbic acid) for the hydroxylating enzymes prolyl hydroxylase and lysyl hydroxylase to function.

Vitamin C deficiency leads to a lack of prolyl and lysyl hydroxylation, making collagen fibers unable to be cross-linked, which decreases the tensile strength of the assembled collagen fiber. This disease is called?

Scurvy

Clinical signs of Scurvy include

Because of the weak collagen structure, patients often have bruises, corkscrew hairs, and perifollicular hemorrhage caused by capillary fragility.

Copper is also a cofactor for lysyl oxidase

EDS arises from;

• lysyl hydroxylase deficiency,

• Procollagen peptidase deficiency,

• Mutations in collagen amino acid sequences, most importantly collagen type III.

• Skin hyperextensibility and joint hypermobility are seen in patients with EDS.

Osteogenesis imperfecta is from a defect of type what collagen?

Type 1 collagen causing brittle bones and blue sclera.

Decreased production of collagen α-chains, leading to bones that are prone to bending and fracture.

Elastin is synthesized from ____________ a precursor protein.

Tropoelastin

After secretion from the cell, tropoelastin deposits onto fibrillin

In the alveoli, elastin is broken down by elastase from activated neutrophils. __________, an enzyme produced in the liver, usually blocks elastase and protects the lungs.

α1-Antitrypsin

Genetic defects in α1-Antitrypsin can lead to ______________at a young age because of increased breakdown of lung connective tissue.

pulmonary emphysema

A higher Km means a (lower/Higher) affinity of the substrate for the enzyme.

Lower

zero-order kinetics.

When [S] > > than Km, the rate of the reaction is independent of [S]

When [S] = Km, then the initial velocity (v) =

Vmax/2

First-order kinetics.

When [S] < Km, the reaction rate is proportional to [S].

Competitive inhibitors

Km is increased, Vmax is unchanged

Noncompetitive inhibitors

Km is unchanged, Vmax is decreased

What is the rate limiting step in the Urea Cycle?

Draw the cycle & name the enzymes in the urea cycle and where the belong. eg mitochondria vs cytosol

What happens with OTC deficiency?

1. Carbamoyl phosphatase 1

2. Carbamoyl phosphatase synthetase 1 —→ Ornithine Transcarbamoylase —→ arginine synthetase ——> Agininesuccinase ——> arginase

3. Increase in Carbamoyl phosphatase and a decrease in citrulline production leading to a impaired urea cycle. Carbamoyl phoaspatsse then creates orotic acid which is toxic

Aminotransferases require ______________ for function

Pyridoxal phosphate (a derivative of vitamin B6)

Amino groups are removed from amino acids by two sequential reactions

1. Transaminases - alanine aminotransferase (ALT) and aspartate aminotransferase (AST), transfer amino groups to α-ketoglutarate, producing an α-keto acid and glutamate. The α-keto acid can enter the citric acid cycle.

2. Glutamate dehydrogenase - oxidatively deaminates glutamate to α-ketoglutarate and free ammonia (NH3)

carbamoyl phosphate synthetase I is activated by

N - acetylglutamate

N-acetylglutamate is synthesized from

acetyl coenzyme A (CoA).

Neomycin and rifaximin orally administered can reduce the number of urease-producing bacteria. They are used to treat what?

Hepatic encephalopathy

Symptoms of hyperammonemia are

Ammonia has a toxic effect on the central nervous system (CNS), causing tremors, cerebral edema, and blurring of vision.

In neonate hyperammonemia during the first weeks after birth. ——————— is common.

Mental retardation

________ can be used to assists in clearance of nitrogen from the blood.

Phenylbutyrate - a prodrug that is metabolized to phenylacetate, combines with glutamine to form phenylacetyl-glutamine

What are the non essential amino acids?

• Arginine

• Alanine

• Asparagine

• Aspartic acid

• Cysteine

• Glutamic Acid

• Glutamine

• Glycine

• Proline

• Serine

• Tyrosine

Aspartate, alanine, and glutamate are synthesized from transamination of α-keto acids. What are they?

• Aspartate is derived from oxaloacetate,

• Glutamate from α-ketoglutarate,

• Alanine from pyruvate.

Glutamine and asparagine are synthesized by amidation.

• Glutamine synthetase forms glutamine from glutamate. This reaction also helps to reduce ammonia levels.

• Asparagine synthetase forms asparagine from aspartate

Serine is synthesized from _______________

Glycine, in turn, can be synthesized from_____________

Proline is synthesized from ___________.

Arginine is synthesized from ___________________

• 3-phosphoglycerate

• Serine.

• Glutamate

• Citrulline

• Cysteine is synthesized from ______ and _____

• Homocysteine is derived from ______________.

• Tyrosine is synthesized from __________ by phenylalanine hydroxylase and BH4 cofactor

1. homocysteine and Serine

2. Methionine

3. Phenylalanine