Formation of vitamin D-binding protein-actin and binary and ternary plasma gelsolin-actin complexes in human serum

After the addition of actin to serum, the binding of actin to serum actin-binding proteins was analyzed by the method of immunoblotting using monospecific antibodies against vitamin D-binding protein (DBP) (group-specific component, Gc), human skeletal actin and human plasma gelsolin. When increasing amounts of globular actin were added to serum, actin bound to DBP preferentially. After exhausting DBP, actin began to bind to plasma gelsolin. When equally increasing amounts of filamentous actin were added to serum, actin was bound to both plasma gelsolin and DBP, and then uncomplexed DBP removed one actin molecule from gelsolin-actin 1:2 complex, resulting in a gelsolin-actin 1:1 complex. These results support the theory that the actin-depolymerizing activity of serum is due to the concerted role of plasma gelsolin and DBP.     

Possible physiological role of guanosine triphosphate and inositol 1,4,5-trisphosphate in Ca2+ release in macrophages stimulated with chemotactic peptide.

The release of Ca2+ induced by inositol 1,4,5-trisphosphate (InsP3) in the presence of GTP was examined by using saponin-permeabilized macrophages. The origin and the amount of mobilized Ca2+ in intact macrophages stimulated with chemotactic peptide were also examined to assess the physiological significance of GTP and InsP3 on Ca2+-releasing activities. The total amount of Ca2+ released by 20 microM-A23187 from the unstimulated intact macrophages was 1.4 nmol/4 x 10(6) cells, and the mitochondrial uncoupler did not cause an efflux of Ca2+ from the cells. The Ca2+ accumulation by the non-mitochondrial pool(s) was inhibited by the presence of GTP, and the total amount of releasable Ca2+ (1.4 nmol/4 x 10(6) cells) was comparable with that accumulated by the non-mitochondrial pool(s) in the presence of GTP at a free Ca2+ concentration of 0.14 microM. The mobilized and subsequently effluxed Ca2+ in cells stimulated with chemotactic peptide was estimated to be 0.3 nmol/4 x 10(6) cells. Much the same amounts were released by about the half-maximal dose of InsP3 from the non-mitochondrial pool(s) of saponin-treated macrophages that had accumulated Ca2+ at a free concentration of 0.14 microM in the presence of GTP. These results suggest that the Ca2+-releasing activity induced by GTP may play a role in the long-term regulation of Ca2+ content in the non-mitochondrial pool(s) of macrophages, and that released by InsP3 can explain, quantitatively, the chemotactic-peptide-induced mobilization of Ca2+.     

Cloning and sequencing of a ligninase gene from a lignindegrading basidiomycete,Phanerochaete chrysosporium

Summary A ligninase gene has been cloned from a Phanerochaete chrysosporium genomic DNA library. Nucleotide sequencing of the gene has revealed that the ligninase structural gene contains 1116 bp of the protein-encoding sequence, of which 84 bp encode the signal peptide. The protein-encoding sequence is interrupted by eight introns which conform to the universal G-T/A-G splicing rule observed for the 3 and 5 intron boundaries. The putative eukaryotic regulatory sequences, i.e. CAAT and TATA box-like sequences, are present in the 5 flanking region.     

Effect of streptozotocin-induced diabetes on the activity of 7 alpha-hydroxy-4-cholesten-3-one-specific 12 alpha-hydroxylase in rats

The activity of 12 alpha-hydroxylase in hepatic microsomes from normal, streptozotocin-induced diabetic, and insulin-treated diabetic rats was studied with 7 alpha-hydroxy-4-cholesten-3-one as a substrate. In the diabetic rats, the 12 alpha-hydroxylase activity was about 50% lower than in the normal rats. Treatment of the diabetics with insulin cancelled the reduction of the activity. These results show that an insulin-deficient state causes a paradoxical decrease in the activity of the key enzyme for cholic acid formation.     

Solubilization and Characterization of Calcitonin Gene-Related Peptide Binding Site from Porcine Spinal Cord

The binding site for calcitonin gene-related peptide (CGRP) was solubilized with 3-[(3-cholamidopropyl)dimethylammonio]-1-propane sulfonate (CHAPS) in an active form from porcine spinal cord. 125I-labeled human alpha-CGRP (125I-CGRP) binding to the solubilized protein was determined by filtration using a GF/B glass filter. The maximal binding activity (approximately 60% of the crude membrane fraction) was obtained with 5 mM CHAPS. 125I-CGRP binding to the solubilized protein was of high affinity, saturability, and high specificity, having KD and Bmax values of 3.69 pM and 338 fmol/mg of protein, respectively. The binding activity was eluted in a single peak with a molecular mass of 400,000 daltons by gel filtration on TSK gel G4000SW. These results suggest that the solubilized protein may be responsible for the specific binding site.     

Membrane-associated nucleoside diphosphate kinase from rat liver. Purification, characterization, and comparison with cytosolic enzyme

Previous studies from this laboratory have proposed that membrane-associated nucleoside diphosphate kinase (m-NDP kinase) may play a role in regulation of adenylate cyclase by channeling GTP, an essential cofactor of adenylate cyclase regulation, into GTP-binding protein (Gs) in a hormone-dependent manner. To understand the true role of m-NDP kinase, in the present study, the m-NDP kinase was solubilized and purified to apparent homogeneity from rat liver purified plasma membranes and characterized in comparison with the cytosolic enzyme purified from the same tissue (s-NDP kinase). Some physical properties determined were: molecular weight (monomer), 18,300; sedimentation coefficient (s20,w), 6.2 S; isoelectric point (pI), 6.0. These values and kinetic parameters of the m-NDP kinase were almost identical to those of the s-NDP kinase whose characteristics were more extensively studied. A peptide mapping study of the 125I-labeled m- and s-NDP kinases gave essentially identical patterns. Polyclonal antibodies against the s-NDP kinase, which also cross-reacted with the m-NDP kinase, were prepared. Immunoblotting studies with the affinity-purified antibodies revealed that the monomer molecular weight of the purified m- and s-NDP kinases was identical to the values of unpurified enzymes present in membranes and crude extract. These results demonstrate that the purified m-NDP kinase underwent no remarkable modification during solubilization and purification, and that the m- and s-NDP kinases are quite similar in protein structure, if at all different. The physiological relevance of the m-NDP kinase in relation to the adenylate cyclase system is discussed.     

Immunocytochemical localization of cathepsins B, H, and their endogenous inhibitor, cystatin beta, in islet endocrine cells of rat pancreas

To determine the characteristics of lysosomes in rat islet endocrine cells, we examined the precise localization of cathepsins B, H, and L and their specific inhibitors, cystatins alpha and beta, using immunocytochemical techniques. By use of serial semi-thin sections, we detected immunoreactivity for cathepsin B in insulin-, glucagon-, somatostatin-, and pancreatic polypeptide-positive (PP) cells. Strong immunoreactivity for cathepsin H was seen in A-cells and weak immunoreactivity in PP cells, but none in others. Immunodeposits for cystatin beta were demonstrated in B-cells. Brief dipping of thin sections in 1% sodium methoxide before the following immunocytochemical reaction enhanced specific deposits of immunogold particles on the target organelles. Use of a double-immunostaining technique showed co-localization of insulin with cystatin beta in many secretory granules. This suggests that cystatin beta may regulate converting enzymes participating in the maturation process of insulin. By use of an immunogold technique, heterogeneous localization of cathepsins B and H in lysosomes was also found among islet cells at the light microscopic level. This may be due to the difference in peptides degraded in lysosomes among the cells.     

Characterization of membrane-bound spermidine dehydrogenase of Citrobacter freundii.

Spermidine dehydrogenase found in the membrane fraction of Citrobacter freundii IFO 12681 was solubilized with Triton X-100 and further purified to homogeneity. The properties of the membrane enzyme were almost identical to those obtained from the soluble fraction of the organism with respect to molecular and catalytic properties. Thus, binding properties of the enzyme to the bacterial membrane were checked. The ratio of enzyme activity found in the soluble fraction to the membrane fraction was dependent on salt concentration during cell disruption. A hydrophobic interaction was largely involved in anchoring the enzyme to the membrane fraction. Purified spermidine dehydrogenase from the soluble fraction was readily adsorbed into the membrane fraction in the presence of salt. Spermidine dehydrogenase appeared to be a membrane-bound enzyme localized in the cytoplasmic membranes in a manner that makes a partial release of the enzyme possible during mechanical cell disruption. When spermidine oxidation was done with the resting cells of C. freundii, a stoichiometric formation of two reaction products, 1,3-diaminopropane and gamma-aminobutyraldeyde, was observed without any lag time. These facts indicate that the enzyme is localized on the outer surface of the cytoplasmic membranes or in the periplasmic space of the organism.