Protein Biochemistry 3

Question 1

What are the sulfur containing amino acids?

Answer 1

Methionine and Cysteine

Question 2

Biological utility of Cys in regard to its oxidative state

Answer 2

the –SH can form disulfides with another Cys, which is important for the structural integrity of many proteins (especially extracellular proteins).

Glutathione (GSH): tripeptide that controls redox potential via GSH←→GSSG, where cysteine is the central amino acid that actually does the work here.

Question 3

Methionine, its relation to SAM, and the energy provided in SAM

Answer 3

Methionine (an essential amino acid) is unique in that it is used to produce S-adenosylmethionine, which is also an intermediate in the production of cysteine.

S-adenosylmethionine (SAM):
Produced in the first step of methionine degradation and converted to S-adenoyslhomocysteine (SAH).

SAM is a major Carbon donor and a “high energy storage unit” like ATP

Question 4

Hyperhomocysteinemia

Answer 4

Elevated levels of homocysteine cause multiple problems that include cardiovascular disease.

Results from low levels of folate, B6, & B12 (vascular disease). Cysteine is now essential and treat with folate, B6, & B12.

Question 5

Homocystinuria

Answer 5

Results from defect in cystathionine-b-synthase (CBS) and cannot convert homocysteine to cystathionine (and eventually cysteine). Leads to mental retardation, osteoporosis, & vascular disease. Cysteine is now essential. Can treat with Vit B6 to “force” CBS activity.

Question 6

Cysteinuria

Answer 6

Kidney stones (renal failure), due to defective in transporter of cysteine (& Ornithine, Lysine, Arginine) that leads to crystallization in urea, treat with acetazolamide that makes cysteine more soluble.

Question 7

Where are vitamins are used in Cysteine and Methionine metabolism?

Answer 7

Folate, B6, B12

Homocysteine→Met needs THF and Vit-B12 to transfer back CH3 group.

Question 8

Biologically important molecules derived from Trp metabolism

Answer 8

Pyruvate or acetyl-CoA

Trp is used to produce serotonin (neurotransmitter), melatonin (hormone), and niacin (energy).

Question 9

Diseases related to Phe,Tyr metabolism

Answer 9

Phenylketonuria (PKU): Defect in phenylalanine hydroxylase that leads to build-up of alternative byproducts (phenyllactate, phenylacetate, and phenylpyruvate).

Tyrosinemia: defects in the mutli-step tyrosine degradation categorized as types I, II, and III that refer to the particular dysfunctional enzyme involved

Parkinson’s Disease (PD)

Use of MonoAmine Oxidase (MAO) inhibitors

Question 10

What cofactors are used for transferring carbons?

Answer 10

SAM

Tetrahydrofolate (THF): donors of one-carbon units in a variety of biosynthetic reactions

Question 11

Glutathione

Answer 11

Redox buffer

Highly soluble tripeptide as opposed to Cys.
As high as millimolar in some tissues.

Functions:

i) thiol acts as redox buffer (“SH buffer”) to maintain proteins in their reduced forms (i.e. intracellular proteins) and regulate activity (i.e. enzymes)
ii) Cofactor for several enzymes (i.e. Glutathione transferase, GST).
iii) Reduce hydrogen peroxide (H2O2) to water and general protection against ROS (radical oxidizing species).

Question 12

Test card

Answer 12

Trying to get the deck to work right