The cysteine proteinase inhibitor chicken cystatin is a phosphoprotein.
Peptide maps obtained by reversed-phase HPLC of tryptic digests of isoelectric form 1 (pI = 6.5) and 2 (pI = 5.6) of chicken egg white cystatin revealed that the difference was located only in a single peptide (residues Ser-74-Lys-91). Ser-80 of cystatin 2 was subsequently identified as being modified by phosphorylation. Moreover, alkaline phosphatase treatment of a mixture of native cystatin forms 1 and 2 was shown by ion-exchange chromatography to cause the disappearance of isoelectric form 2 with a concomitant increase in form 1. Thus, the existence of two isoelectric forms of chicken cystatin is due to the phosphorylated form 2 and non-phosphorylated form 1.
Laber
B
B
Max-Planck-Institut für Biochemie, Martinsried, FRG.
Krieglstein
K
K
Henschen
A
A
Kos
J
J
Turk
V
V
Huber
R
R
Bode
W
W
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002645:Chickens; D002851:Chromatography, High Pressure Liquid; D015891:Cystatins; D015853:Cysteine Proteinase Inhibitors; D006868:Hydrolysis; D007525:Isoelectric Focusing; D008969:Molecular Sequence Data; D010449:Peptide Mapping; D010750:Phosphoproteins / Q000032:analysis*; D011506:Proteins / Q000032:analysis*; D014357:Trypsin
D000596:Amino Acids; D015891:Cystatins; D015853:Cysteine Proteinase Inhibitors; D010750:Phosphoproteins; D011506:Proteins; C100158:cystatin, egg-white; D014357:Trypsin