Higazi A A, Finci-Yeheskel Z, Samara A A, Aziza R, Mayer M
Department of Clinical Biochemistry, Hadassah Medical Center, Jerusalem, Israel.
Biochem J. 1992 Mar 15;282 ( Pt 3)(Pt 3):863-6. doi: 10.1042/bj2820863.
The amidolytic activity of plasmin with the chromogenic substrate H-D-valyl-L-leucyl-L-lysine p-nitroanilide (S-2251) is stimulated by oleic acid in a dose-dependent and saturable fashion. The activity of plasmin on S-2251 in the presence of oleic acid followed a sigmoidal kinetic pattern, with an almost 4-fold stimulation of activity at 60 microM-oleic acid. Half-maximal stimulation occurred at an oleic acid level of 19.5 microM. The amino acid analogue 6-aminohexanoic acid (AHA), which is known to bind to lysine-binding sites in plasmin, suppressed the stimulatory effect of oleic acid in a concentration-dependent manner; at 0.3 mM-AHA, about 70% of the oleic acid-dependent enhancement of plasmin activity was abolished. The l/v versus 1/[S] plot for plasmin changed in the presence of oleic acid from a linear to a non-linear curve, suggesting positive co-operativity. 14C-labelled oleic acid bound to plasmin, and the bound ligand was displaced by an excess of unlabelled oleic acid. Oleic acid also produced a marked (40-fold) stimulation of the plasminogen-dependent cleavage of S-2251 by urokinase. A half-maximal effect on plasminogen activation was obtained at 40 microM-oleic acid. The present findings suggest that the ability of oleic acid to stimulate plasmin activity and to enhance the conversion of plasminogen to plasmin depends on the interaction of oleic acid with specific lysine-binding sites in plasmin.
纤溶酶对生色底物H-D-缬氨酰-L-亮氨酰-L-赖氨酸对硝基苯胺（S-2251）的酰胺分解活性受到油酸的刺激，呈剂量依赖性且具有饱和性。在油酸存在下，纤溶酶对S-2251的活性遵循S形动力学模式，在60μM油酸时活性几乎增强4倍。在油酸水平为19.5μM时出现半数最大刺激。已知能与纤溶酶中赖氨酸结合位点结合的氨基酸类似物6-氨基己酸（AHA）以浓度依赖性方式抑制油酸的刺激作用；在0.3 mM AHA时，约70%的油酸依赖性纤溶酶活性增强被消除。在油酸存在下，纤溶酶的l/v对1/[S]图从线性变为非线性曲线，表明存在正协同性。14C标记的油酸与纤溶酶结合，且结合的配体可被过量的未标记油酸置换。油酸还对尿激酶介导的S-2251的纤溶酶原依赖性裂解产生显著（40倍）刺激。在40μM油酸时获得对纤溶酶原激活的半数最大效应。目前的研究结果表明，油酸刺激纤溶酶活性和增强纤溶酶原向纤溶酶转化的能力取决于油酸与纤溶酶中特定赖氨酸结合位点的相互作用。
