Molecular characterization of 1,4-dihydropyridine-sensitive calcium channels of chick heart and skeletal muscle

A monoclonal antibody designated as MAC-L1 immunoprecipitated [3H]PN200-110-labeled calcium channels of chick cardiac and skeletal muscle. On specific immunoprecipitation of 125I-labeled proteins, two large polypeptides (Mr 197,000 and 139,000 for heart, and 172,000 and 135,000 for skeletal muscle, under reducing conditions) were identified as the major components of these channels. Both polypeptides were found to exist together as a complex in 1% digitonin, but to become separated from each other in 1% Triton X-100. The 197 and 172 kDa peptides of cardiac and skeletal muscles, respectively, were photolabeled with [3H]azidopine. Under nonreducing conditions, the 139 kDa polypeptide of heart and the 135 kDa polypeptide of skeletal muscle took on larger molecular weights of 192,000 and 190,000, respectively. The 139 kDa but not the 197 kDa component of the heart was capable of binding to wheat germ agglutinin-Sepharose. Among the polypeptides specifically precipitated by MAC-L1, a 165 kDa peptide of skeletal muscle was phosphorylated by cAMP-dependent protein kinase. In contrast, a minor 99 kDa polypeptide, but not the major 197 kDa polypeptide, of the heart was phosphorylated by this kinase. These results suggest that the dihydropyridine-sensitive cardiac calcium channel has alpha 1 and alpha 2 subunits that are homologous but not identical to those of the skeletal muscle calcium channel.     

Isolation and characterization of new cross-linking amino acid "allodesmosine" from hydrolysate of elastin

A new pentafunctional cross-linking amino acid, termed allodesmosine, was isolated from bovine ligamentum nuchae elastin. This compound was a very hygroscopic, white amorphous solid with a faint yellow tinge, soluble in aqueous solvents but not dry methanol; it was characterized by UV, FAB mass and NMR spectroscopy. The compound was shown by UV and 1H-NMR to have a pyridinium ring structure similar to desmosine. Mass spectral analysis indicated a parent compound with a mass of 655. We postulated that it arose by condensation of a reduced aldol condensation product of allysine, allysine and lysine.     

Macrophage activation for tumor cytotoxicity: Control of cytotoxic activity by the time interval effector and target cells are exposed to lymphokines

Macrophages continuously exposed to lymphokines (LK) and target cells throughout a 48-hr cytotoxicity assay exhibit 3-fold more tumoricidal activity than do cells optimally treated with LK before addition of tumor cells. Increased cytotoxic activity induced by continuous LK treatment was not due to direct toxic effects of LK on tumor target cells or to alterations in target cell susceptibility to cytopathic effects of LK-activated macrophages. Moreover, sensitivities of responsive macrophages to LK activation signals and time courses for onset and loss of tumoricidal activity during continuous exposure or LK pulse were identical. Analysis of macrophage or LK dose responses and time courses for development of cytotoxicity each suggest that differences in tumoricidal activity between macrophages continuously exposed or pulsed with LK were quantitative: the number of cytotoxic events was increased 2.7 ± 0.2-fold (mean ± SEM for 11 experiments) during continuous LK treatment. Optimal levels of macrophage tumoricidal activity then occur only if effector cells, target cells and activation stimuli are simultaneously present for a defined time interval: tumor cells need not be present during the initial 2 to 3 hr of culture; LK can be removed after 8 hr with little or no loss of cytotoxic activity. However, removal of LK or target cells during the critical 4- to 8-hr interval decreased levels of cytotoxicity 3-fold. Thus, nonspecific effector function by LK-activated macrophages in controlled by both the physicochemical nature of the LK mediator and the time interval effector and target cells are exposed to LK.     

Migration of IgA-bearing lymphocytes into salivary glands

The relative migratory properties of [¹²⁵I]iododeoxyuridine-labeled dividing mesenteric lymph node (MLN) and peripheral lymph node (PLN) cells were assessed in mice using the adoptive transfer system. MLN cells from virgin donors showed a greater tendency to localize in MLN, small intestine, and mammary glands (lactating recipients only) of virgin and lactating recipients. In addition, MLN cells were shown to selectively localize in the salivary (submandibular and sublingual) glands. The relative migratory properties of MLN and PLN cell populations were identical when donor cells were obtained from virgin or lactating animals. Selective depletion of IgA-bearing cells from the MLN transfer cell population abrogated the preferential localization in control mucosal tissues and salivary glands. These data show that the salivary glands can be included as an additional mucosal area populated by gut-derived IgA-bearing cells and provides direct evidence that the common mucosal immune sytstem extends to secretory tissue in the oral cavity.     

The effect of alpha2-macroglobulin from bovine serum on bovine alpha-chymotrypsin.

Bovine alpha2-globulin contains a protein which increases the activity of bovine alpha-chymotrypsin against synthetic substrates. The active protein fraction migrates slowly on polyacrylamide gel electrophoresis, so it was named slow alpha2-globulin (Salpha2). The fraction was isolated from bovine serum and purified. Its sedimentation constant S20 was 18.5 S. It was thus identified with the alpha2-macroglobulin (alpha2M). By kinetic studies, the dissociation constant of the alpha-chymotrypsin-alpha2 M complex was calculated to be of the order of 10(-7) l/mol. The purified alpha2 M was shown to bind alpha-chymotrypsin at a definite rate. If the binding ratio was assumed to be 1:2, the molecular weight was calculated to be about 8 X 10(5).     

Alpha reduced nicotinamide adenine dinucleotide-dependent reductase reactions of rat liver microsomes.

The kinetics of alpha-NADH-dichlorophenolindophenol (DCPIP) and alpha-NADH-cytochrome c reductase reactions of rat liver microsomes showed that the reactio ns proceeded by a ping-pong mechanism, and that the oxidation of alpha-NADH was the rate-determining reaction. The DCPIP-reducing activity with alpha-NADH in the presence of ADP was about 1% of that with beta-NADH. ADP inhibited the alpha-NADH-DCPIP reductase reaction in a competitive manner with respect to alpha-NADH and a value of 1.2 mM for the inhibition constant was obtained. ADP also inhibited cytochrome b5 reduction with alpha-NADH. More than 90% of cytochrome b5 was reduced under conditions where 90% of the alpha-NADH-DCPIP reductase activity was suppressed with ADP. The reduction of DCPIP with alpha-NADH preceded that of cytochrome b5, but the reductions partly overlapped. From these results, a diversed electron flow from alpha-NADH to cytochrome b5 and electron sharing between cytochrome b5 and DCPIP were indicated. alpha-NAD+ also inhibited the alpha-NADH-DCPIP reductase reaction. Analyses of the inhibition indicated that two types of alpha-NADH-DCPIP reductase reaction existed, one of which was resistant to alpha-NAD+ inhibition. In contrast to the reoxidation of beta-NADH-reduced cytochrome b5, the process was largely monophasic when cytochrome b5 was reduced with alpha-NADH.     

Molecular cloning and expression analysis of novel wheat cysteine protease

A cDNA clone encoding a novel papain-like cysteine protease was isolated from wheat germ (Triticum aestivum). This cDNA encoded a 371-residue protein, designated WCP2, composed of signal peptide followed by a propeptide and a mature protease containing active site residues that are highly conserved among the papain family. The mature WCP2 protein (26 kDa) was detected in the quiescent embryo and its level of expression in the germinating embryo was greatly increased.     

Identification of a fibroblast-derived epithelial morphogen as hepatocyte growth factor.

We have previously shown that Madin-Darby canine kidney (MDCK) epithelial cells grown in collagen gels in the presence of fibroblasts or fibroblast-conditioned medium (CM) form branching tubules, instead of the spherical cysts that develop under control conditions. We now report that the fibroblast-derived molecule responsible for epithelial tubulogenesis is hepatocyte growth factor (HGF). First, addition of exogenous HGF to cultures of MDCK cells induces formation of epithelial tubules. Second, the tubulogenic activity of fibroblast CM is completely abrogated by antibodies to HGF. These results demonstrate that HGF, a polypeptide that was identified as a mitogen for cultured hepatocytes, has the properties of a paracrine mediator of epithelial morphogenesis, and suggest that it may play important roles in the formation of parenchymal organs during embryonic development.     

Colcemid treatment of myeloma prior to cell fusion increases the yield of hybridomas between myeloma and splenocyte

Effect of Colcemid treatment of myeloma (X63-Ag8-6.5.3.) prior to fusion with mouse spleen cell was studied in terms of hybridoma formation. Spleen cells from BALB/c mice immunized with various soluble antigens were fused with the myeloma cells by using polyethylene glycol solution. Colcemid treatment of myeloma cells prior to fusion increased the average number of hybridoma colonies per well by 26-570%. The yield of hybridomas producing antigen-specific antibodies was also higher with the Colcemid treatment. The results suggest that most of the proliferative hybridomas are formed by fusion of cells in the M-phase of the cell cycle.