Binding of tissue-type plasminogen activator (t-PA) to Neisseria meningitidis and Haemophilus influenzae

Abstract Forty-nine bacterial strains representing five species known to interact with human plasminogen were tested for the ability to bind the two major human plasminogen activators, t-PA and urokinase. The bacterial species tested included Haemophilus influenzae, Neisseria meningitidis, Streptococcus pyogenes, Streptococcus equisimilis and human group G streptococci. All N. meningitidis and 11 of 14 H. influenzae strains displayed substantial binding of t-PA with values in the range of 20–46%. On the contrary, none of the streptococcal strains bound significant amounts of tPA. With urokinase no binding could be found for any of the bacterial species tested. Scatchard analysis with a selected H. influenzae strain (HI23354) demonstrated 10 000 receptors per bacterium for t-PA with a K _d value of about 20 nmol l⁻¹. The corresponding values with a selected N. meningitidis strain (Mo 52) was 8500 receptors per bacterium and 70 nmol l⁻¹. t-PA binding could be reduced about 40% by the addition of 10 nmol l⁻¹ of the lysine analogue ϵ-aminocaproic acd (EACA) whereas no inhibitory effect could be demonstrated with arginine. Addition of 2 μmol l⁻¹ of plasminogen which is enough to occupy all bacterial sites for plasminogen did not interfere with the t-PA binding, suggesting that the receptors for t-PA and plasminogen are distinct. Using very high plasminogen concentrations however, t-PA binding could be reduced by about 50% possibly due to an interaction between t-PA and plasminogen in the fluid phase. Our results demonstrate the occurrence of a previously unknown type of bacterial receptor that is capable of specifically binding t-PA.     

On the biological significance of the specific interaction between fibrin,plasminogen and antiplasmin

The influence of antiplasmin on the interaction between fibrin and plasminogen was studied in plasma and in a purified system. The amount of plasminogen bound to fibrin was quantitated using trace amounts of ¹²⁵I-labeled Glu-plasminogen (plasminogen with NH₂-terminal glutamic acid) or ¹²⁵I-labeled Lys-plasminogen (NH₂-terminal lysine).When whole plasma was clotted, 5.2% of Glu-plasminogen was associated with the fibrin clot. In plasma clotted in the presence of 20 mM 6-amino-hexanoic acid only 1.4% of the plasminogen was bound to fibrin, indicating that about 4% of the plasma plasminogen specifically binds to fibrin. With Lys-plasminogen these values were approximately twice as high.When antiplasmin-depleted plasma was used, only slightly higher amounts of both types of plasminogen were associated with the fibrin. The adsorbed plasminogen was not significantly eluted with plasma or with purified antiplasmin at physiological concentrations.These findings indicate that antiplasmin does not play a significant role in the inhibition of the binding of plasminogen to fibrin or the dissociation of the plasminogen · fibrin complex.These observations in conjunction with previous findings on the kinetics of the plasmin-antiplasmin reaction suggest that the lysine-binding site of plasminogen, which is responsible both for its interaction with fibrin and its interaction with antiplasmin, plays an important role in the very fast neutralization of plasmin formed in circulating blood and serves to attach plasminogen to fibrin and thereby sequestrate plasmin formed in loco from circulating antiplasmin.     

Complex formation between plasminogen activator inhibitor 1 and vitronectin in purified systems and in plasma

Functionally active PAI-1 is bound to a discrete binding or carrier protein in plasma, which was recently identified as vitronectin. In the present study, the interaction between PAI-1 and vitronectin has been studied in purified systems and in plasma by agarose gel electrophesis using non-denaturing conditions and by crossed immunoelectrophoresis using an antiserum produced towards purified PAI-1/vitronectin complex. Both methods revealed a clearly distinguishable complex with electrophoretic mobility in between the parent molecules. Virtually all of the purified vitronectin, which did not contain any appreciable amounts of polymerized material, and almost all of the vitronectin in plasma, had the capacity to form a complex with PAI-1. The results suggested a stoichiometry of 1:1 as the most likely ratio between the two molecules in the complex. In contrast to functionally active PAI-1, latent or chloramine T-inactivated PAI-1 did not form such a complex with vitronectin.     

AN EXPERIMENTAL APPROACH TO THE SYSTEMATICS OF THE MONOECIOUS-CONJOINED MEMBERS OF THE GENUS CHARA,SERIES GYMNOBASALIA

Most monoecious-conjoined members of the series Gymnobasalia, genus Chora, bear either tetrascutate or octoscutate antheridia. A determination of the extent to which various populations of these two morphologically distinct entities are reproductively isolated was the primary objective of the present study. Experimental crosses were attempted between emasculated sprigs and nonemasculated plants serving as sperm sources. All evidence suggests that tetra- and octoscutate populations are reproductively isolated throughout their respective ranges even to the extent of producing black oospores. Crosses were also attempted between geographically isolated tetrascutate, and again octoscutate, populations. All were uniformly successful to the extent that black oospores resulted; but when such oospores were germinated many of the resulting progeny were found to be either nonviable or dwarfed, and frequently self-sterile as well. This was particularly true where parental clones differed with respect to geographical origin, chromosome number, or external morphological features.