fch 532 lecture 27 chapter 26: essential amino acids
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Table 26-2 Essential and Nonessential Amino Acids in Humans. Page 1030TRANSCRIPT
FCH 532 Lecture 27 Chapter 26: Essential amino acids
Quiz Wed: NIH Shift Quiz Mon: Essential amino acids Exam 3: Next
Wed. Table 26-2 Essential and Nonessential Amino Acids in
Humans.
Page 1030 Glutamate is the precursor for Proline, Ornithine, and
Arginine
E. coli pathway from Gln to ornithine and Arg involves ATP-driven
reduction of the glutamate gamma carboxyl group to an aldehyde
(N-acetylglutamate-5-semialdehyde). Spontaneous cyclization is
prevented by acetylation of amino group by N-acetylglutamate
synthase. N-acetylglutamate-5-semialdehyde is converted to amine by
transamination. Hydrolysis of protecting group yields ornithine
which can be converted to arginine. In humans it is direct from
glutamate-5-semialdehyde to ornithine by
ornithine--aminotransferase Arginine synthesis glutamyl kinase 6.
Acetylglutamate kinase
N-acetyl--glutamylphosphate dehydrogense
N-acetylornithine--aminotransferase Acetylornithine deacetylase
ornithine--aminotransferase Urea cycle to arginine Page 1036
Conversion of 3-phosphoglycerates 2-OH group to a ketone
Figure The conversion of glycolytic intermediate 3-phosphoglycerate
to serine. Conversion of 3-phosphoglycerates 2-OH group to a ketone
Transamination of 3-phosphohydroxypyruvate to 3-phosphoserine
Hydrolysis of phosphoserine to make Ser. Page 1037 Serine is the
precursor for Gly
Ser can act in glycine synthesis in two ways: Direct conversion of
serine to glycine by hydroxymethyl transferase in reverse (also
yields N5, N10-methylene-THF) Condensation of the N5,
N10-methylene-THF with CO2 and NH4+ by the glycine cleavage system
Cys derived from Ser In animals, Cys is derived from Ser and
homocysteine (breakdown product of Met). The -SH group is derived
from Met, so Cys can be considered essential. Methionine
adenosyltransferase Methyltransferase
Adenosylhomocysteinase Methionine synthase (B12) Cystathionine
-synthase (PLP) Cystathionine -synthase (PLP) -ketoacid
dehydrogenase Propionyl-CoA carboxylase (biotin) Methylmalonyl-CoA
racemase Methylmalonyl-CoA mutase Glycine cleavage system or serine
hydroxymethyltransferase N5,N10-methylene-tetrahydrofolate
reductase (coenzyme B12 and FAD) Page 1002 Cys derived from Ser In
plants and microorganisms, Cys is synthesized from Ser in two step
reaction. Reaction 1: activation of Ser -OH group by converting to
O-acetylserine. Reaction 2: displacement of the acetate by sulfide.
Sulfide is derived fro man 8-electron reduction reaction. Figure
26-59a. Cysteine biosynthesis
Figure 26-59aCysteine biosynthesis. (a) The synthesis of cysteine
from serine in plants and microorganisms. Page 1038 Sulfite to
sulfide by sulfite reductase
Figure 26-59bCysteine biosynthesis. (b) The 8-electron reduction of
sulfate to sulfide in E. coli. Sulfate activation by ATP sulfuylase
and adeosine-5-phosphosulfate (APS) kinase Sulfate reduced to
sulfite by 3-phosphoadenosine-5-phosphosulfate (PAPS) reductase
Sulfite to sulfide by sulfite reductase Page 1038 Biosynthesis of
essential amino acids
Pathways only present in microorganisms and plants. Derived from
metabolic precursors. Usually involve more steps than nonessential
amino acids. Biosynthesis of Lys, Met, Thr
First reaction is catalyzed by aspartokinase which converts
aspartate to apartyl--phosphate. Each pathway is independently
controlled. Figure The biosynthesis of the aspartate family of
amino acids: lysine, methionine, and threonine. Page 1039 Figure
The biosynthesis of the pyruvate family of amino acids: isoleucine,
leucine, and valine. Page 1040 Figure 26-62The biosynthesis of
chorismate, the aromatic amino acid precursor.
Page 1042 Figure 26-63The biosynthesis of phenylalanine,
tryptophan, and tyrosine from chorismate.
Page 1043 Figure 26-64A ribbon diagram of the bifunctional enzyme
tryptophan synthase from S. typhimurium
Page 1044 Figure 26-65 The biosynthesis of histidine.
Page 1045