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PubMed1983

Differential effects of phospholipids on skeletal alkaline phosphatase activity in extracts, in situ and in circulation.

Human skeletal alkaline phosphatase (ALP) purified from human bone was subject to competitive inhibitions by phospholipids including cephalins, lecithins, and phosphatidylinositol. Ki values ranged from 0.7 to 1.5 mM, at pH 9.5. As previously shown, the enzyme was subject to uncompetitive inhibition by imidazole. The inhibitory phospholipids potentiated this effect, and altered the nature of the imidazole inhibition, from uncompetitive to mixed type, suggesting that imidazole was bound more efficiently to the enzyme-phospholipid complex than to the enzyme-substrate complex. No interactions were observed between phospholipids and other uncompetitive inhibitors of ALP. The skeletal ALP activity of cultured chick calvarial cells was assayed both in situ and in extracts. Like the extracted human isoenzyme, the extracted chick ALP was subject to competitive inhibition by cephalin (Ki = 0.3 mM at pH 9.3) and an inhibitory interaction between cephalin and imidazole, but the same isoenzyme showed neither effect in situ. The value of Km,PNPP at pH 9.5 for chick skeletal ALP was 1.5 mM in extracts and 7.1 mM in situ. When embryonic chick bones were cultured in vitro, skeletal ALP activity was released into the serum-free medium. Unlike the same isoenzyme extracted from the bones, the ALP activity in the medium was not inhibited by cephalin and showed no inhibitory interaction between cephalin and imidazole. Similarly, human serum ALP activities were not as sensitive to phospholipid inhibition as the same isoenzymes extracted from tissues. Human skeletal ALP extracted from bone was inhibited by cephalin, but the skeletal isoenzyme in Pagetic serum was not, suggesting that the potential for phospholipid interaction was altered during or after release from osteoblast cell membranes. The observation that extracted human skeletal ALP lost its potential for inhibition by phospholipids after treatment with phospholipase C further suggests that ALP activity may be released from cells during membrane turnover.

Alkaline Phosphatase↗
PubMed1984

Phospholipids accelerate factor IX activation by surface bound factor XIa.

Activation of bovine factor IX by surface bound factor XIa which was generated either by activation of human citrated factor IX deficient plasma or a mixture of purified human factors XII, high molecular weight kininogen (HMWK) and XI in glass tubes, is accelerated by cephalin. Human brain cephalin in dilutions ranging from 1:5 to 1:500 was studied for its effect on the activation of factor IX in concentrations of 1.0 u/ml and 16 u/ml. Cephalin dilutions from 1:5 to 1:30 accelerated the activation of the concentrated factor IX sample two- to threefold. Protein cleavage of this factor IX sample in the presence of 1:30 cephalin occurred twice as fast as in the absence of cephalin. Activation of the dilute factor IX sample (1.0 u/ml) was most effectively accelerated by cephalin in dilutions from 1:30 to 1:250. In all experiments the presence of phospholipid led to an increased factor IX cleavage concomitantly with faster generation of factor IXa activity. The results demonstrate that phospholipids actively participate in blood coagulation at an earlier stage than previously described.

Animals↗
PubMed1964

REACTION OF LOCAL ANESTHETICS WITH PHOSPHOLIPIDS. A POSSIBLE CHEMICAL BASIS FOR ANESTHESIA.

Local anesthetics (LA) have been found to interact with phospholipids and lipids extracted from nerve and muscle. This reaction is demonstrated by: (a) Inhibition by LA of phospholipid (and tissue lipid) facilitated transport of calcium from a methanol: water phase into chloroform. This action is dependent upon the cationic form of the LA. (b) LA increase the electrical resistance of "membranes" prepared by impregnating Millipore filters with cephalin:cholesterol or tissue lipid extracts and bathed with NaCl or KCl solutions. (c) LA coagulate aqueous dispersions of cephalin, phosphatidyl serine, phosphatidyl ethanolamine, and inositide, an action shared by calcium. The order of potency in coagulating cephalin sols is tetracaine > calcium > butacaine > procaine. Na(+) and K(+) do not coagulate phospholipid dispersions at 0.1 M concentration and antagonize the effect of Ca(2+). (d) LA produce a marked fall in the pH of cephalin sols equivalent to that produced by calcium, (e) Ca(2+) and LA form 1:2 molar complexes with phospholipids probably by ion-ion and ion-induced polar type of binding at the phosphate groups of the lipid. It is suggested that such reactions with cell membrane phospholipids may underlie inhibitory effects of LA on cellular ion fluxes and provide a chemical basis for anesthetic action.

Alcohols↗
PubMed1991

Shared idiotypic determinant in mono- and polyclonal anti-phospholipid antibodies with lupus anticoagulant activity.

Of 42 purified human myeloma proteins tested, two (IgG3 Her and IgM Mag) were found to possess strong lupus anticoagulant (LA) and anti-cephalin activity, as assessed by a dilute activated partial thromboplastin time (dAPTT) and ELISA test, respectively. For these proteins, we confirmed the observation reported by others that LA activity is present in the antigen-binding (Fab) portion of the immunoglobulin molecule. Rabbit anti-idiotype antibodies against IgG3 Her inhibited the anti-cephalin activity of this protein, suggesting that the anti-cephalin activity of IgG3 Her depends on the hypervariable part of the immunoglobulin and thus most probably is a true antigen-antibody reaction. The anti-Her idiotype antibodies were also able to bind to and inhibit the anti-cephalin activity of IgM Mag. ELISA binding and inhibition experiments showed that the anti-idiotype antiserum contained at least two sets of anti-idiotypes; one set that recognizes a cross-reactive idiotype shared by IgG3 Her and IgM Mag, and another set that seems to be unique to the immunizing protein IgG3 Her. Both sets of anti-idiotype antibodies also bound weakly to polyclonal (patient) IgG, indicating an idiotypic cross reaction.

Antibodies, Anti-Idiotypic↗
PubMed1998

Isolation of a protein Z-dependent plasma protease inhibitor.

Human protein Z (PZ) is a 62,000-Mr, vitamin K-dependent plasma protein whose structure is similar to coagulation factors VII, IX, X, protein C, and protein S, but whose function is not known. The procoagulant activity of factor Xa in a one-stage plasma coagulation assay is reduced when factor Xa is first incubated with PZ. This apparent inhibitory effect is time dependent, requires the presence of calcium ions and procoagulant phospholipids (rabbit brain cephalin), and appears predominantly related to the incubation period of PZ with cephalin. In serum the initial rate of inhibition of factor Xa with calcium ions and cephalin also is enhanced in the presence PZ. A PZ-dependent protease inhibitor (ZPI) has been isolated from plasma. ZPI is a 72,000-Mr single-chain protein with an N-terminal amino acid sequence of LAPSPQSPEXXA (X = indeterminate) and an estimated concentration in citrate-treated plasma of 1.0-1.6 microg/ml. In systems using purified components, the factor Xa inhibition produced by ZPI is rapid (>95% within 1 min by coagulation assay) and requires the presence of PZ, calcium ions, and cephalin. The inhibitory process appears to involve the formation of a factor Xa-PZ-ZPI complex at the phospholipid surface.

Amino Acid Sequence↗