Purification from Synaptosomal Plasma Membranes of Calpain I, a Thiol Protease Activated by Micromolar Calcium Concentrations

Synaptosomal plasma membranes (SPMs) were prepared from whole rat brain and assayed for calcium-stimulated proteolytic activity. Addition of calcium to SPMs caused a dose-dependent increase in trichloroacetic acid-soluble protein. Two peaks of protease activity directed against a casein substrate were detectable when SPMs were incubated with low-ionic-strength buffer and the extract was fractionated on DEAE-cellulose. The enzyme in peak 1 required less than 1/10 the calcium concentration for activation as the peak 2 protease (Kact1 = 35 microM; Kact2 = 500 microM). The specific thiol-protease inhibitors leupeptin and antipain and the alkylator iodoacetate blocked enzyme activity. The low-sensitivity protease was converted to a high-sensitivity enzyme (Kact = 20 microM) by substrate affinity chromatography in the presence of calcium. This protease was purified 550-fold from SPMs. The high- and low-sensitivity membrane-associated calcium-dependent proteases are part of a family of enzymes, the calpains, previously reported in cytosolic fractions of several tissues.     

Thermotropic lipid phase separations in human platelet and rat liver plasma membranes

Electron spin resonance (ESR) studies were conducted on human platelet plasma membranes using 5-nitroxide stearate, I(12,3). The polarity-corrected order parameter S and polarity-uncorrected order parameters S(T parallel) and S(T perpendicular) were independent of probe concentration at low I(12.3)/membrane protein ratios. At higher ratios, S and S(T perpendicular) decreased with increasing probe concentration while S(T parallel) remained unchanged. This is the result of enhanced radical interactions due to probe clustering. A lipid phase separation occurs in platelet membranes that segregates I(12,3) for temperatures less than 37 degrees C. As Arrhenius plots of platelet acid phosphatase activity exhibit a break at 35 to 36 degrees C, this enzyme activity may be influenced by the above phase separation. Similar experiments were performed on native [cholesterol/phospholipid ratio (C/P) = 0.71] and cholesterol-enriched [C/P = 0.85] rat liver plasma membranes. At 36 degrees C, cholesterol loading reduces I(12,3) flexibility and decreases the probe ratio at which radical interactions are apparent. The latter effects are attributed to the formation of cholesterol-rich lipid domains, and to the inability of I(12,3) to partition into these domains because of steric hinderance. Cholesterol enrichment increases both the high temperature onset of the phase separation occurring in liver membranes from 28 degrees to 37 degrees C and the percentage of probe-excluding, cholesterol-rich lipid domains at elevated temperatures. A model is discussed attributing the lipid phase separation in native liver plasma membranes to cholesterol-rich and -poor domains. As I(12,3) behaves similarly in cholesterol-enriched liver and human platelet plasma membranes, cholesterol-rich and -poor domains probably exist in both systems at physiologic temperatures.     

Kinetics of dissociation of reduced nicotinamide adenine dinucleotide phosphate from its complexes with malic enzyme in relation to substrate inhibition and half-of-the-sites reactivity

Malic enzyme of pigeon liver binds NADPH at four equivalent enzyme sites and binds Mn2+ and malate each at two sets of "tight" and "weak" sites with negative cooperativity [Pry, T. A., & Hsu, R. Y. (1980) Biochemistry 19, 951-962]. Stopped-flow studies on the displacement of NADPH from the malate-enzyme complexes E4-NADPH4, E4-Mn2(2+)-NADPH4, E4-Mn2(2+)-NADPH4-dimalate, and E4-Mn2(2+)-NADPH4-tetramalate by large excess NADP+ or its analogue phosphoadenosine(2')diphospho(5')ribose show that NADPH dissociates from the binary complex rapidly with a first-order rate constant of 427 s-1. Dissociation from the ternary E4-Mn2(2+)-NADPH4 complex containing two tightly bound Mn2+ ions can be described by a single first-order process with a rate constant of 135 s-1, or more satisfactorily by two simultaneous first-order processes attributable to the reactions of Mn2+-deficient (k congruent to 427 s-1) and Mn2+-liganded (k = 96 s-1) subunits. The latter equals twice the maximum steady-state turnover rate of 53.2 + 3.0 s-1 assigned to dissociation of the reduced nucleotide from transient E-Mn2+-NADPH, and this 2:1 ratio strongly supports our proposed "half-of-the-sites" model [Hsu, R. Y., & Pry, T. A. (1980) Biochemistry 19, 962-968]. Dissociation from the E4-Mn2(2+)-NADPH4-dimalate complex (k = 100 s-1) follows only the slower process, suggesting that occupancy of malate at two sites tightens enzyme-bound NADPH on the adjacent sites. Binding of malate at two additional weak sites yields E4-Mn2(2+)-NADPH4-tetramalate and a NADPH dissociation rate constant of 2.69 s-1. The 97% decrease in NADPH dissociation parallels the observed 93% maximal inhibition by malate and is the cause of substrate inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)     

Dinitrophenyl-pepstatins as active-site-directed localization reagents for cathepsin D

1. N-Pepstatinyl-N'-dinitrophenyl-1,6-diaminohexane, a potential active-site-directed localization reagent for cathepsin D, was found to bind non-specifically to immuno-precipitates containing cathepsin D. 2. Three new water-soluble localization reagents were synthesized, by using NN'-bis-(3-aminopropyl)piperazine, 3-oxa-1,5-diamino-pentane or 3,6-dioxa-1,8-diamino-octane, as spacer arms between the pepstatin and dinitrophenyl moieties. 3. The hydrophilic dinitrophenyl-pepstatins were all tight-binding inhibitors of cathepsin D at pH 3.5, but showed little or no binding to immuno-precipitates containing the inactive enzyme at pH 7.4. 4. Gel-chromatographic experiments showed that, at pH 5.0, all the dinitrophenyl-pepstatins were bifunctional reagents able to bind cathepsin D and anti-dinitrophenyl antibody at the same time. Enzyme-inhibitor-antibody complexes were not formed at pH 7.4, thus confirming that the reagents were active-site-directed. 5. Cultured human synovial cells were fixed and incubated with the dinitrophenyl-pepstatins at pH 5.0 or pH 7.4. After washing briefly, the cells were incubated at the appropriate pH value with anti-dinitrophenyl antibody labelled with fluorescein. When examined by fluorescence microscopy the cells stained at pH 5.0 showed fluorescent perinuclear granules, which were not seen in the cells treated at pH 7.4. The distribution of cathepsin D, determined by indirect immuno-fluorescence at pH 7.4, closely resembled that revealed by the dinitrophenyl-pepstatins at pH 5.0. 7. NN'-(3-Pepstatinylaminopropyl-3'-dinitrophenylaminopropyl)piperazine gave the most intense lysosomal staining and showed no non-specific binding. We conclude that this reagent is suitable for the subcellular localization of the active conformation of cathepsin D.     

MICROTUBULE PROTEIN : Identification in and Transport to Nerve Endings

The subunit protein of microtubules, tubulin, has been demonstrated to be present in isolated nerve endings by gel electrophoresis, amino acid composition, and peptide mapping. The tubulin constitutes approximately 28% of the soluble protein of the nerve endings. The transport of tubulin to the nerve endings has been demonstrated and its relationship to slow transport is discussed.     

CYTOKINESIS AND PLASMODESMATA IN ULOTHRIX1

Cytokinesis essentially similar to that of vascular plants occurs in Ulothrix, an unbranched filamentous green alga. Plasmodesmata, similar to those of vascular plants, but different from those of many other algae, are also present. Cell plate formation and plasmodesmata also occur in Stigeoclonium, a branched green alga.     

Australia Antigen and Liver Function Tests Following Infectious Hepatitis—A Study of 111 Patients in Quest of Aids in Blood Donor Screening

An epidemic of infectious hepatitis involving 99 patients and employees of a state mental hospital revealed Australia antigen Au(1) to be absent from the blood of all but one of the subjects when tested at six weeks, three months, nine months and 12 to 18 months after onset of jaundice. The single patient with Au(1) at 12 months had no enzyme abnormality to indicate residual liver disease.If Au(1) is the virus of hepatitis these data would support the concept that persistent or long standing viremia is not a feature of epidemic hepatitis. Moreover, results of this study suggest that the Au(1) test should not be used to establish the absence of a past history of hepatitis in blood donors. These data do not establish the value of the Au(1) test in blood donors with active viremia, but do suggest that of 111 patients with recent hepatitis 1 percent had persistent antigenemia and 4 percent probably had circulating antigen antibody complexes and constituted a potential risk to recipients of their blood. The degree of risk to recipients from transfused blood of post-hepatitis patients without demonstrable Au(1) cannot be assessed.     

Inhibition of Transformation of Bacillus subtilis by Heavy Metals

Mercuric ions, as well as organomercuric ions and cadmium ions, can inhibit deoxyribonucleic acid-mediated transformation in Bacillus subtilis 168 without decreasing the viability of the total population. Differences in the inhibition of transformation by mercuric ions are identifiable on a temporal and concentration dependence basis. Sensitivity to low concentrations (9.2 x 10(-8) M) appears early in the uptake of deoxyribonucleic acid before the transformed markers have become insensitive to deoxyribonuclease. Resistance to "low concentrations" of Hg(2+) is kinetically indistinguishable from the requirement for magnesium in the transformation process. This inactivation is not reversed by the mercury-binding compound glutathione. Sensitivity to mercuric ions at a higher concentration (5.52 x 10(-7) M) occurs after the donor deoxyribonucleic acid has become insensitive to deoxyribonuclease. These complex interactions between mercuric ions and the process of transformation are discussed.