Function of streptokinase fragments in plasminogen activation.
Several peptide fragments of streptokinase (SK) were prepared by incubating SK with immobilized human plasmin (hPlm) and purified by h.p.l.c. with a reverse-phase phenyl column. The N-terminal sequences, amino acid compositions and molecular masses of these peptide fragments were determined. The SK peptide fragment of 36 kDa consisting of Ser60-Lys387 (SK-p), was the only peptide fragment that could be tightly bound to immobilized hPlm. Another three large SK peptide fragments, SK-m, SK-n and SK-o, with molecular masses of 7 kDa, 18 kDa and 30 kDa, and consisting of Ile1-Lys59, Glu148-Lys333, Ser60-Lys333 respectively, were also obtained from the supernatant of the reaction mixture. The purified SK-p had high affinity with hPlm and could activate human plasminogen (hPlg) with a kPlg one-sixth that of the native SK. SK-o had low affinity with hPlm and could also activate hPlg, although the catalytic constant was less than 1% of the native SK. SK-n, as well as SK-m, which is the N-terminal 59 amino acid peptide of the native SK, had no activator activity. However, SK-m could enhance the activator activity of both SK-o and SK-p and increase their second-order rate constants by two- and six-fold respectively. It was concluded from these studies that (1) SK-o, the Ser60-Lys333 peptide of SK, was essential for minimal SK activator activity, (2) the C-terminal peptide of SK-p, Ala334-Lys387, was essential for high affinity with hPlm, and (3) the N-terminal 59-amino-acid peptide was important in maintaining the proper conformation of SK to have its full activator activity.
Shi
G Y
GY
Department of Biochemistry, Medical College, National Cheng Kung University, Tainan, Taiwan, Republic of China.
Chang
B I
BI
Chen
S M
SM
Wu
D H
DH
Wu
H L
HL
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002417:Cattle; D002851:Chromatography, High Pressure Liquid; D006801:Humans; D007700:Kinetics; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010446:Peptide Fragments / Q000737:chemistry / Q000302:isolation & purification; D010958:Plasminogen / Q000737:chemistry*; D010960:Plasminogen Activators / Q000737:chemistry*; D011487:Protein Conformation; D013300:Streptokinase / Q000737:chemistry* / Q000494:pharmacology
D010446:Peptide Fragments; D010958:Plasminogen; D013300:Streptokinase; D010960:Plasminogen Activators