Phagocytosis in human platelets: localization of acid phosphatase-positive phagosomes following latex uptake

Incubation of human platelets in plasma containing a suspension of latex particles for 1-90 min resulted in progressive accumulation of particles in the open-channel system, followed by localization of latex in electron-opaque vacuoles. After 60 min, acid phosphatase was localized within latex-containing vacuoles. The periodate-alkaline-bismuth reaction intensely stained external membranes and membranes of the open-channel system. Membranes of latex-containing organelles were not stained. Latex phagocytosis was independent of both anticoagulant choice and aspirin effects. Our results indicate that the platelet can act as a true phagocyte, and we suggest that the phagocytic process is chronologically similar to that reported for polymorphonuclear leukocytes.

Characteristics of the association between prothrombin fragment 2 and alpha-thrombin

The esterolytic activity of bovine alpha-thrombin on the synthetic substrate N-alpha-p-tosyl-L-arninine methyl ester (TosArgOMe) is stimulated when the prothrombin activation fragment, prothrombin fragment 2, is added as previously reported by this laboratory (Heldebrant, C. M., and Mann, K. G. (1973), J. Biol. Chem. 248, 3642). A similar stimulation of beta-thrombin is observed upon addition of prothrombin fragment 2. The binding constant of prothrombin fragment 2 to alpha-thrombin has been determined by the method of Gutfreund ((1972), Enzymes, Physical Principles, Wiley, New York, N.Y., pp 67-71). The dissociation constant is 7.7 X 10(-10)M, and there is one molecule of prothrombin fragment 2 bound per molecule of alpha-thrombin. Prethrombin-2 competes for prothrombin fragment 2, so the enhancement of the esterolytic activity of alpha-thrombin by prothrombin fragment 2 was used as a probe to determine the dissociation constant for the binding of prothrombin fragment 2 to prethrombin 2. The dissociation constant for this association is 1.3 X 10(-10)M. The kinetic parameters for the reaction of alpha-thrombin on TosArgOMe were determined in the absence and presence of prothrombin fragment 2 and are as follows: (a) in the absence of prothrombin fragment 2, Km(app) = 1.92 X 10(-4)M, and k3(app) = 35.8 mol of TosArgOMe/mol of alpha-thrombin s(-1); (b) in the presence of prothrombin fragment 2,Km(app = 1.76 X 10(-4)M, and k3(app) = 60.5 mol of TosArgOMe/mol of alpha-thrombin s(-1). Thus, the stimulatory effect of bovine prothrombin fragment 2 on bovine alpha-thrombin is reflected in k3(app) and not in Km(app). In contrast to the stimulatory effect of prothrombin fragment 2 on the thrombin-catalyzed hydrolysis of TosArgOMe, it inhibits the activity of alpha-thrombin toward N-alpha-benzoyl-L-arginine ethyl ester and N-alpha-benzoyl-L-arginine p-nitroanilide. The inhibition of activity toward these substrates by prothrombin fragment 2 is also reflected in k3(app). Activity toward the nonspecific substrate p-nitrophenyl butyrate was completely inhibited by the addition of prothrombin fragment 2. Prothrombin fragment 2 has no effect on the inhibition of alpha-thrombin activity by the active-site serine inhibitors diisopropyl phosphofluoridate, phenylmethanesulfonyl fluoride, or p-nitrophenyl guanidinobenzoate. Inhibition by the active-site-histidine-modifying inhibitor, N-alpha-p-tosyl-L-arginine chloromethyl ketone, was enhanced by the addition of prothrombin fragment 2. Soybean trypsin inhibitor reduces the stimulation by prothrombin fragment 2, but only at high molar ratios. Prothrombin fragment 2 has no effect on the clotting activity of alpha-thrombin, nor inhibition of this activity by heparin, hirudin, or diisopropyl phosphafluoridate. Bovine prothrombin fragment 2 enhances the esterolytic activity of both human and bovine alpha-thrombin, but human prothrombin fragment 2 does not enhance the esterolytic activity of either human or bovine alpha-thrombin.

Comparative properties of the Charcot-Leyden crystal protein and the major basic protein from human eosinophils

Guinea pig eosinophil granules contain a protein, the major basic protein (MBP), which accounts for more than half of the total granule protein, has a high content of arginine, and displays a remarkable tendency to form disulfide-linked aggregates. In this study we have purified a similar protein from human eosinophil granules and have compared the human MBP to the protein comprising the Charcot-Leyden crystal (CLC). Eosinophils from patients with various diseases were purified and disrupted, and the granule fraction was obtained. Examination of the granule fraction by transmission electron microscopy showed numerous typical eosinophil granules. Analyses of granule lysates by gel filtration and by polyacrylamide gel electrophoresis revealed the presence of peroxidase and MBP with properties similar to that previously found in guinea pig eosinophil granules. The human MBP had a molecular weight of 9,200, contained less than 1% carbohydrate, was rich in arginine, and readily formed disulfide-bonded aggregates. CLC were prepared from eosinophil-rich cell suspensions by homogenization in hypotonic saline. The supernates following centrifugation of cell debris spontaneously formed CLC. Analysis of CLC revealed the presence of a protein with a molecular weight of 13,000 containing 1.2% carbohydrate. The protein displayed a remarkable tendency to aggregate even in the presence of 0.2 M acetic acid. Human MBP and CLC protein differed in their molecular weights, carbohydrate compositions, and amino acid analyses. Mixtures of the MBP and the CLC protein yielded two bands in polyacrylamide gel electrophoresis. Neither eosinophil protein increased vascular permeability in the guinea pig skin or contracted the guinea pig ileum. The results indicate that the human MBP and the CLC are distinct substances with properties such that one cannot be derived from the other.

Studies on IgA and IgA monoclonal proteins derived from a single patient. Evidence for identical light chains and variable regions of the heavy chain

Two immunoglobulins, IgA(K) and IgG(K), were isolated from the serum of a single patient with two monoclonal components (biclonal proteins). After chain separation, the light chains from each molecule were found to be identical by the following criteria: electrophoretic mobilities under various pH and dissociating conditions, amino acid compositon, fingerprint analysis of tryptic peptides and of 14C-succinylated chymotryptic peptides, and amino acid sequence of the N-terminal 40 residues. The heavy chains were indistinguishable for the N-terminal 45 amino acid residues. These data are consistent with the hypothesis that a single heavy chain variable (VH) region may be associated with two different heavy chain constant (CH) genes.

Human prothrombin activation

Human prothrombin has been purified from American Red Cross Factor IX concentrates. Studies of the activation of the human prothrombin with the use of sodium dodecyl sulfate electrophoretic analysis of activation products indicated that human prothrombin activation is similar to bovine prothrombin activation. Molecular weight analysis of human prothrombin and intermediated by sodium dodecyl sulfate co-electrophoresis with bovine prothrombin and its intermediates resulted in molecular weights of 70,000 for prothrombin, 51,000 for intermediate 1, 41,000 for intermediate 2, 23,000 for intermediate 3, and 13,000 for intermediate 4. Amino acid compositions of human prothrombin and intermediates are similar to those for bovine prothrombin and intermediates. NH2-terminal sequence studies of human prothrombin, intermediates, and alpha-thrombin A and B chains placed the intermediates in the parent human prothrombin molecule as described for the bovine system. Intermediate 3 is the NH2-terminal of prothrombin, and intermediate 1 is the COOH-terminal segment of the zymogen. Intermediate 4 is the NH2-terminal of intermediate 1. Intermediate 2', the immediate precursor of alpha-thrombin, is the COOH-terminal segment of intermediate 1. In general, a high degree of homology in the primary structure of prothrombin and intermediates was observed between the human and bovine system. The NH2-terminal sequences of human intermediate 2' and alpha-thrombin A chain are identical. However, human intermediate 2' isolated in a manner identical with that used for the isolation of bovine intermediate 2 is homologous with bovine intermediate 2, beginning with residue 14.

Chemical and physical studies on the structure of Escherichia coli elongation factor G

Elongation Factor G (EF-G) from Escherichia coli was purified to homogenity by a previously published method (Rohrbach, M. S., Dempsey, M. E., and Bodley, J. W. (1974) J. Biol. Chem. 249, 5094). The protein is composed of a single polypeptide chain of molecular weight 74,000 under native conditions and 71,000 under denatured conditions as determined by high speed equilibrium centrifugation. An apparent molecular weight of 73,000 was found by sodium dodecyl sulfate gel electrophoresis. The protein has an apparent alpha helix content of 34% as determined from its circular dichroism spectrum. The extinction coefficient at 280 nm was found to be 62,200 M-1 cm-1. Lysine is the COOH-terminal residue and the sequence at the NH2 terminus is alanylarginine. No evidence of terminal heterogeneity was observed. The amino acid composition of EF-G revealed no unusual amino acids or prosthetic groups, but was notable in that the protein contains only 6 cysteine residues. The maintenance of at least one of these cysteines in the reduced form is essential for activity, since the protein is rapidly inactivated upon removal of protecting thiol. Under some conditions, activity can be partly restored by re-addition of a thiol. The per cent activity of the protein was examined by an active site titration, the formation of the EF-G-ribosome-GDP-fusidic acid complex. The formation of 1 mol of complex/mol of EF-G showed that the protein is 100% active.

Prothrombin fragments. Ca2+ binding and activation kinetics

The binding of Ca2+ to prothrombin and the intermediates of prothrombin activation was investigated by equilibrium dialysis using 45Ca2+ as the ligand. Scatchard plots of these data indicate that prothrombin (Mr = 70,000) has 10 to 11 Ca2+ binding sites which can be differentiated in terms of their binding affinity. Six of these Ca2+ binding sites have log Kassoc = 3.5 and all are found intact in the NH2-terminal segment (activation intermediate 3, Mr = 23,000) of the prothrombin molecule. Four or five additional weaker binding sites for Cz2+ with log Kassoc = 2.7 present in prothrombin are found intact in the remaining COOH-segment (activation intermediate 1, Mr = 51,000) of the prothrombin molecule. Upon further activation the Ca2+ binding sites residing in intermediate 1 are found intact in activation intermediate 4 (which constitutes the NH2-terminal segment of the intermediate 1 molecule). The remaining COOH-terminal portion (activation intermediate 2, Mr = 41,000) of the intermediate 1 molecule has no affinity for Ca2+. The activation of prothrombin and activation intermediates 1 and 2 was studied using these activators: Factor Xa alone, Factor Xa-Ca+, AND Factor Xa-Ca2+-phospholipid. The rate of thrombin production from prothrombin was progressively increased as Ca2+ and phospholipid were added to the system, whereas no significant increase in the rates of activation of intermediate 1 and 2 was observed. When Factor V was added to the Factor Xa-Ca2+-phospholipid system, the rate of activation of intermediate 1 was greatly enhanced. In the absence of Ca2+, Factor V had no effect on the rate of thrombin formation from intermediate 1. Factor V had no stimulatory effects on the rate of intermediate 2 activation. However, in the presence of an equimolar amount of intermediate 4, Factor V accelerated the conversion of intermediate 2 to thrombin. These studies indicate that the Ca2+ binding sites of the prothrombin molecule are contained in the "pro" fragment (intermediates 3 and 4) of the prothrombin molecule. Intermediate 1 and intermediate 2, both of which lack the strong Ca2+ binding sites of prothrombin, are poor substrates for the Factor Xa-Ca2+-phospholipid complex activation when compared to prothrombin. The addition of Factor V to the catalyst results in acceleration of the activation rate of intermediate 1 and an equimolar mixture if intermediates 2 and 4. These results lead us to conclude that the strong Ca2+ binding sites are the sites of phospholipid binding (intermediate 3), whereas the seak binding sites are the sites of Factor V binding (intermediate 4).

Physiochemical and biological properties of the major basic protein from guinea pig eosinophil granules

Guinea pig eosinophil granules are characterized by the presence of a basic protein of low molecular weight which accounts for greater than 50% of granule protein. This protein, termed the major basic protein (MBP), readily aggregates and becomes insoluble, and the formation of aggregates is dependent on the establishment of disulfide bonds. Analysis of concentrated preparations of MBP often revealed a series of bands which were multiples of a monomeric unit with a mol wt of approximately 11,000. Analysis of reduced and alkylated MBP on a 10% agarose column equilibrated with 6 M guanidinium chloride revealed a single polypeptide chain with a mol wt of 10,800. Amino acid analysis of the protein revealed the presence of 13% arginine, consistent with the basic character of the molecule. Four residues of tryptophan, were present, indicating that MBP is not a histone. The MBP did not increase vascular permeability when injected into the skin of guinea pigs, nor did it antagonize the effect of histamine and bradykinin in the skin. MBP also did not contract the isolated guinea pig ileum and when mixed with histamine or bradykinin did not inhibit their activity on the gut. MBP had only weak, if any, antihistaminic activity. MBP possessed weak bactericidal activity when compared to histone and then only with one strain of E. coli. MBP precipitated DNA, neutralized heparin, and activated papain. On a molar basis MBP was more active than cysteine in activating papain. These results do not point to any unique biological activity associated with MBP other than those expected of a protein as basic as it is and one which possesses reactive sulfhydryl groups. Possible functions of eosinophils based on the properties of the MBP are discussed.