ORGANIC CHEMISTRY 3540

POLYPEPTIDES

CLASSIFICATION

NOMENCLATURE

STRUCTURE

STRUCTURE DETERMINATION

PREPARATION

PEPTIDE CLASSIFICATION:

DIPEPTIDE - 2 AMINO ACIDS

TRIPEPTIDE - 3 AMINO ACIDS

DECAPEPTIDE - 10 AMINO ACIDS

OLIGOPEPTIDE - 2 TO 10 AMINO ACIDS

POLYPEPTIDE - 10+ AMINO ACIDS

PROTEIN - MOLECULAR WEIGHT OVER 10,000

NOMENCLATURE

EXAMINE BONDING (INTERACTIVE)

POLYPEPTIDES!

DETERMINATION OF AMINO ACID SEQUENCE

EDMAN DEGRADATION

SANGER METHOD

CARBOXYPEPTIDASE A

EVENTUALLY SUCH END GROUP ANALYSIS FAILS DUE TO INCREASING HYDROLYSIS WITHIN THE PEPTIDE CHAIN.

• DO A TOTAL HYDROLYSIS
  • DETERMINE THE TOTAL NUMBER OF EACH AMINO ACID

• DO A PARTIAL HYDROLYSIS
  • ISOLATE FRAGMENTS
  • SEQUENCE FRAGMENTS
  • PUT FRAGMENTS BACK TOGETHER

EXAMPLE

SELECTIVE HYDROLYSIS

• CHYMOTRYPSIN
  • CATALYZES HYDROLYSIS OF THE -CO₂H END OF
    • PHENYLALANINE
    • TYROSINE
    • TRYPTOPHAN

• TRYPSIN
  • CATALYZES HYDROLYSIS OF THE -CO₂H END OF
    • ARGININE
    • LYSINE

• BrCN (CYANOGEN BROMIDE)
  • CATALYZES HYDROLYSIS OF THE -CO₂H END OF
    • METHIONINE

• ILLUSTRATION

• EXAMPLE

LABORATORY SYNTHESIS OF PEPTIDES

• MAKE AMIDES

• NEED TO PROTECT THE AMINO GROUP WITH AN EASILY REMOVED GROUP.
  • CARBOBENXOXY GROUP

• MANY OTHER TECHNIQUES INCLUDING ATTACHING DEVELOPING PEPTIDE TO A SOLID RESIN FOR EASY PURIFICATION AND TRANSFERS