Effects of acidic phospholipids, nucleotides, and heparin on the activity of lipase from rat liver lysosomes

Purification and characterization of endogenous lipid factors that stimulate rat liver lysosomal lipase has led to the identification of cardiolipin, phosphatidylserine, and phosphatidic acid as stimulators of this activity. Bovine heart cardiolipin (half-maximal stimulation at 1.5 x 10(-4) m) and bovine brain phosphatidylserine (half-maximal stimulation at 9.5 x 10(-4) m) were the most potent of the phospholipids from other sources tested. The major rate-enhancing effect of phosphatidylserine is expressed as a 35-fold increase in the apparent V(max) of the enzyme. The effect is produced by acid phospholipids specifically, since in no case was there greater than a twofold stimulation by synthetic detergents, zwitterionic phospholipids, taurocholic acid, or gum acacia. The observed degree of stimulation depends upon the detergent used to disperse tripalmitin substrate and the relative concentrations of factor and detergent in reaction mixtures. The concentration of phosphatidylserine to produce half-maximal stimulation is directly dependent upon the Triton X-100 concentration, but the effects of this detergent on cardiolipin stimulation are more complex. Enzyme activity is inhibited 50% by 1 mm nucleoside triphosphate and 2.5 mm ADP, 80% by 1 mm PP(i), 100% by 20 U/ml heparin and 0.25 mg/ml chondroitin sulfate, and 80% by 10 mm sulfate ion. Inhibition is partially prevented by phosphatidylserine.

Effect of Sodium Chloride Salinity on the Water Balance of Atriplex Halimus

Sodium chloride was found to improve the water balance of A. halimus plants under conditions of high evaporative demand. This improvement was expressed by higher values of turgor pressure and percentage saturation value in plants grown in salinized culture solutions (Knop solution to which sodium chloride was added to give final osmotic potentials of from -3 to -10 bars) as compared with plants grown in the control (Knop) solutions.

Alteration in Complement Component Utilization Following the Interaction of C1̄hu with a Kallikrein Fragment

A mixture of human IgG, kallikrein and plasma thromboplastin antecedent (PTA) prepared by passage of serum over DEAE-cellulose equilibrated with 0.01 m phosphate buffer, pH 8, was found to enhance the hemolytic activity of activated human first component of complement (C1̄hu). Fractionation of this mixture on Sephadex G-150 revealed peaks of C1̄hu-enhancing activity at 45% bed volume, the position of kallikrein, and at 80% bed volume. Repeat filtration of the kallikrein fraction on Sephadex G-150 yielded the low molecular weight C1̄hu-enhancing factor, suggesting that it was derived from kallikrein. This non-dialyzable fragment lacked kallikrein activity and unlike C1̄s did not split N-α-acetylglycyl-l-lysine methylester (AGLMe), N-acetyl-l-arginine methylester (AAMe), p-tosyl-l-arginine methylester (TAMe), N-acetyl-l-tyrosine methylester (ATMe), the fourth component (C4), or the second component (C2).

Kinetics of C2 activation by C1̄ acting upon EAC42 prepared with limited concentrations of unactivated C2 indicated that C1̄ containing 20 mol/cell produced 0.57 SAC with a tmax of 3.5 min; C1̄ acted upon by the fragment and then diluted sevenfold as compared to the untreated C1̄ produced 1.6 SAC at a tmax of 1.75 min.

Interaction of beef liver lipase with mixed micelles of tripalmitin and Triton X-100

When concentrated dispersions of tripalmitin in Triton X-100 are added to reaction mixtures containing soluble beef liver lipase, the rate of hydrolysis of tripalmitin increases with incubation time. When the diluted substrate is aged at 37 degrees C for 3 hr before the addition of enzyme, the rate of hydrolysis is greater than the rate with freshly diluted dispersions and is constant for at least 2 hr. The reciprocal of the rate of hydrolysis is a complex function of the reciprocal of the substrate concentration when measured with freshly diluted substrate dispersions. A linear relationship between these reciprocals is obtained when measured with aged preparations of substrate. The rate and extent of increase of the velocity of hydrolysis of the aged substrate in relation to the velocity of hydrolysis of freshly diluted substrate are directly proportional to the substrate concentration and inversely proportional to the Triton X-100 concentration. The apparent V(max) of beef liver lipase for tripalmitin in diluted and aged dispersions is independent of the Triton X-100 concentration, while the apparent K(m) is inversely proportional to the Triton X-100 concentration. The apparent K(m) for tripalmitin complexes at zero Triton X-100 concentration was judged to be 7.5 x 10(-5) m. The molecular size of dispersion complexes does not change significantly as dispersions are aged. The spherical diameter of the complexes assessed by gel filtration techniques is in the order of 100 A.