Extracts from the bacterium Bacillus brevis contain a peptide with antibiotic properties. This peptide forms complexes with metal ions and seems to disrupt ion transport across the cell membranes of other bacterial species, leading to bacterial death. The structure of the peptide has been determined from a series of observations. (a) Complete acid hydrolysis of the peptide, followed by amino acid analysis, yielded equimolar amounts of Leu, Orn, Phe, Pro, and Val. Orn is ornithine, an amino acid not present in proteins but present in some peptides. Orn has the structure H 'H,N-CH, - CH2 CH2 CH2 - C - COO- NH, (b) The molecular weight of the peptide is approximately 1,200 Da. (c) The peptide failed to undergo hydrolysis when treated with the enzyme carboxypeptidase. This enzyme catalyzes the hydrolysis of the carboxyl-terminal residue of a polypeptide unless the residue is Pro or the peptide does not contain a free carboxyl group. (d) Treatment of the intact peptide with 1-fluoro-2,4-dinitrobenzene (FDNB), followed by complete hydrolysis and chromatography, yielded only free amino acids and the derivative shown here. O,N NO₂ H NH— CH, - CH₂- CH₂ - - C - COO- +NH3 (Hint: The 2,4-dinitrophenyl derivative involves the amino group of a side chain rather than the a-amino group.) (e) Partial hydrolysis of the peptide followed by chromatographic separation and sequence analysis yielded these di- and tripeptides (the amino-terminal amino acid is always the first amino acid): Leu-Phe Phe-Pro Orn-Leu Val-Orn Val-Orn-Leu Phe-Pro-Val Pro-Val-Orn Given this experimental information, deduce the amino acid sequence and the structure of the peptide antibiotic. Orn Leu Val Pro Phe linear peptide of Leu-Phe-Pro-Val-Orn Leu Orn Phe Val Pro + Pro Val Phe Orn Leu linear peptide of Pro-Val-Orn-Leu-Phe-Pro-Val-Orn-Leu-Phe-Pro linear peptide of Leu-Phe-Pro-Val-Orn-Leu-Phe-Pro-Val-Orn
Extracts from the bacterium Bacillus brevis contain a peptide with antibiotic properties. This peptide forms complexes with metal ions and seems to disrupt ion transport across the cell membranes of other bacterial species, leading to bacterial death. The structure of the peptide has been determined from a series of observations. (a) Complete acid hydrolysis of the peptide, followed by amino acid analysis, yielded equimolar amounts of Leu, Orn, Phe, Pro, and Val. Orn is ornithine, an amino acid not present in proteins but present in some peptides. Orn has the structure H 'H,N-CH, - CH2 CH2 CH2 - C - COO- NH, (b) The molecular weight of the peptide is approximately 1,200 Da. (c) The peptide failed to undergo hydrolysis when treated with the enzyme carboxypeptidase. This enzyme catalyzes the hydrolysis of the carboxyl-terminal residue of a polypeptide unless the residue is Pro or the peptide does not contain a free carboxyl group. (d) Treatment of the intact peptide with 1-fluoro-2,4-dinitrobenzene (FDNB), followed by complete hydrolysis and chromatography, yielded only free amino acids and the derivative shown here. O,N NO₂ H NH— CH, - CH₂- CH₂ - - C - COO- +NH3 (Hint: The 2,4-dinitrophenyl derivative involves the amino group of a side chain rather than the a-amino group.) (e) Partial hydrolysis of the peptide followed by chromatographic separation and sequence analysis yielded these di- and tripeptides (the amino-terminal amino acid is always the first amino acid): Leu-Phe Phe-Pro Orn-Leu Val-Orn Val-Orn-Leu Phe-Pro-Val Pro-Val-Orn Given this experimental information, deduce the amino acid sequence and the structure of the peptide antibiotic. Orn Leu Val Pro Phe linear peptide of Leu-Phe-Pro-Val-Orn Leu Orn Phe Val Pro + Pro Val Phe Orn Leu linear peptide of Pro-Val-Orn-Leu-Phe-Pro-Val-Orn-Leu-Phe-Pro linear peptide of Leu-Phe-Pro-Val-Orn-Leu-Phe-Pro-Val-Orn
Chapter9: Parenteral Medication Labels And Dosage Calculation
Section: Chapter Questions
Problem 6.7P
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Transcribed Image Text:Extracts from the bacterium Bacillus brevis contain a peptide with antibiotic properties. This peptide forms complexes with
metal ions and seems to disrupt ion transport across the cell membranes of other bacterial species, leading to bacterial death.
The structure of the peptide has been determined from a series of observations.
(a) Complete acid hydrolysis of the peptide, followed by amino acid analysis, yielded equimolar amounts of Leu, Orn, Phe, Pro,
and Val. Orn is ornithine, an amino acid not present in proteins but present in some peptides. Orn has the structure
H
'H,N-CH,
-
CH2 CH2 CH2 -
C - COO-
NH,
(b) The molecular weight of the peptide is approximately 1,200 Da.
(c) The peptide failed to undergo hydrolysis when treated with the enzyme carboxypeptidase. This enzyme catalyzes the
hydrolysis of the carboxyl-terminal residue of a polypeptide unless the residue is Pro or the peptide does not contain a free
carboxyl group.
(d) Treatment of the intact peptide with 1-fluoro-2,4-dinitrobenzene (FDNB), followed by complete hydrolysis and
chromatography, yielded only free amino acids and the derivative shown here.
O,N
NO₂
H
NH— CH, - CH₂- CH₂
-
-
C - COO-
+NH3
(Hint: The 2,4-dinitrophenyl derivative involves the amino group of a side chain rather than the a-amino group.)
(e) Partial hydrolysis of the peptide followed by chromatographic separation and sequence analysis yielded these di- and
tripeptides (the amino-terminal amino acid is always the first amino acid):
Leu-Phe
Phe-Pro
Orn-Leu
Val-Orn
Val-Orn-Leu
Phe-Pro-Val
Pro-Val-Orn
Given this experimental information, deduce the amino acid sequence and the structure of the peptide antibiotic.
Orn
Leu
Val
Pro
Phe
linear peptide of Leu-Phe-Pro-Val-Orn
Leu
Orn
Phe
Val
Pro
+
Pro
Val
Phe
Orn
Leu
linear peptide of Pro-Val-Orn-Leu-Phe-Pro-Val-Orn-Leu-Phe-Pro
linear peptide of Leu-Phe-Pro-Val-Orn-Leu-Phe-Pro-Val-Orn
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