Conformational study of 13C-enriched fibroin in the solid state, using the cross polarization nuclear magnetic resonance method

Silk fibroin with the alanyl carboxyl carbon enriched with 13C was obtained by giving a diet containing 13C-enriched alanine to the larvae of Bombyx mori and Antheraea pernyi at the fifth instar. Sericin-free fibroin fibers were prepared from cocoons, and gut was made from the liquid silk in the gland. The final 13C content was about 13%. Cross polarization/magic angle sample spinning spectra at 25 MHz and 75 MHz were measured for each sample at different orientations. Spectra were simulated using the principal values and orientations of the shielding tensor in the alanine crystal. The results indicate that the beta-structure of the fibroin may be a little more flattened than the typical pleated sheet beta-structure.     

Additive stimulation of hepatic putrescine production by glucagon and insulin after partial hepatectomy in rats

When rats received glucagon or insulin every 2 h after partial hepatectomy (Hx), hepatic putrescine content was increased above control levels at 6 and 12 h, respectively. When the two hormones were combined, the increased levels were additive. Hepatic ornithine decarboxylase activity was above control levels at 12 h after insulin treatment. Hepatic spermidine N1-acetyltransferase activity was enhanced at 6 h only when glucagon was dosed. Putrescine administration from 0 to 4 h or from 6 to 10 h increased hepatic DNA synthesis to similar levels 22 h after Hx. These results suggest that glucagon and insulin additively stimulate hepatic putrescine production after Hx. This may explain the cooperative stimulation of liver regeneration by both hormones.     

Characterization of adenylate and guanylate cyclases in rat peritoneal mast cells

Adenylate and guanylate cyclase activities were confirmed in crude homogenates from rat peritoneal mast cells. Both enzyme activities were associated with the 105, 000 X g particulate fractions, but not detected in the supernatant fractions. The optimal pH for both cyclase activities was 8.2. Mn⁺⁺ was essentially required for guanylate cylcase activity, while adenylate cyclase activity was observed in the presence of either Mg⁺⁺ or Mn⁺⁺. The apparent Km values of adenylate cyclase for Mn⁺⁺-ATP and Mg⁺⁺-ATP were 160 μM and 340 μM, respectively, whereas the value of guanylate cyclase for Mn⁺⁺-GTP was 100 μM. Adenylate cyclase was activated by 10 mM NaF. However, both adenylate and guanylate cyclase activities were neither stimulated nor inhibited by the addition of various kinds of agents which stimulate or inhibit the release of histamine from mast cells.     

Analysis of mutations in cyclodextrin glucanotransferase from Bacillus stearothermophilus which affect cyclization characteristics and thermostability.

Cyclodextrin glucanotransferase (CGTase; EC 2.4.1.19) produces cyclodextrin from starch. The CGTase molecule is composed of four globular domains, A, B, C, and D. In order to gain better understanding of the amylolytic and cyclization mechanisms of CGTase, mutant CGTases were constructed from a CGTase gene (cgt1) of Bacillus stearothermophilus NO2. Cgt1-F191Y (Phe at position 191 was replaced by Tyr), Cgt1-F191Y-F255Y, Cgt1-W254V-F255I, Cgt1-W254V, and Cgt1-F255I were constructed for the analysis of the NH2-terminal region. It was revealed that amino acids surrounding a spiral amylose are important for cyclization characteristics and that hydrophobic amino acids just after the Glu catalytic site play an important role in the hydrolysis characteristics of the enzyme. Mutant CGTases Cgt1-T591F and Cgt1-W629F were also constructed to study the role of a second substrate-binding site in domain D, and it was suggested that substrate binding at both domains A and D stabilized the enzyme and optimized cyclodextrin production.     

The augmentation of tumor-specific immunity using haptenic muramyl dipeptide (MDP) derivatives

Summary A new haptenic compound, a muramyl dipeptide (MDP) derivative (designated as L4-MDP-ONB) cross-reactive with Bacillus Calmette Guerin (BCG) was synthesized. The cross-reactivity of L4-MDP hapten to BCG was demonstrated from the following evidence; (a) lymph node cells from BCG-primed C3H/HeN mice exhibited appreciable L4-MDP-specific proliferative responses to the in vitro stimulation of L4-MDP-modified syngeneic cells (L4-MDP-self); (b) inoculation of L4-MDP-self into footpads of BCG-primed C3H/HeN mice elicited ample delayed type-hypersensitivity (DTH) responses in vivo as measured by footpad swelling; and (c) BCG-primed mice contained L4-MDP-reactive helper T cell activity which functions to augment the generation of effector T cell responses to cell surface antigens. This crossreactivity between L4-MDP hapten and BCG as measured by the helper T cell activity was applied to enhanced induction of tumor-specific immunity. When BCG-primed C3H/HeN mice were immunized with L4-MDP-modified syngeneic X5563 tumor cells, these mice could generate augmented tumor-specific in vivo protective (tumor neutralizing) immunity as well as in vitro cytotoxic T cell responses. These results indicate the effectiveness of L4-MDP hapten in augmenting tumor-specific immunity. The present approach is discussed in the context of potential advantages of this new hapten for its future application to clinical tumor systems.     

Single-locus control of the mast cell population in mouse skin

The number of mast cells in connective tissue from dorsal skin varied markedly among mouse strains. Inbred strains of mice were typed into three groups, high (NC and NZB mice), low (B6, B10, and BALB/c mice), and intermediate (C3H/He and DBA/2 mice), by their mast cell content in the skin. However, the strain differences in the number of mast cells was marginal at the age of weaning but became distinct with age. This could be explained mainly by the frequently observed clustering of mast cells in adult NC and NZB mice and the rarely observed clustering in younger mice as well as in adult B10 and BALB/c mice. The breeding experiment revealed that the difference in the number of mast cells between NC and B10 mice was controlled by a single autosomal dominant locus, for which we propose the designation Mcr (mast cell regulator). The role of the Mcr locus with regard to the frequency of the mast cell population in connective tissue is discussed.     

Effects of barbiturates on the inhibitory action of GABA on excitatory response of the stomach to stimulation of vagal afferent fibers in cat

Effects of barbiturates on the inhibitory action of GABA to the hexamethonium-resistant excitatory response of the stomach to stimulation of the vagal afferent fibers were studied in cats. Inhibition of the hexamethonium-resistant excitatory response by GABA were compared under alpha-chloralose, alpha-chloralose-phenobarbital (PhB), and alpha-chloralose-pentobarbital (PB)-anesthesia in cats. The ID50 of GABA on the hexamethonium-resistant excitatory response was not significantly affected by PhB, but reduced by PB. Both picrotoxin and bicuculline antagonized the effects of GABA. The present experiments demonstrated that PB potentiated the inhibitory effect of GABA on the hexamethonium-resistant excitatory response of the stomach, and suggested that the potentiation by PB may be due to activation of GABA-receptor-ionophore complex.     

Preferential synthesis of diacyl and alkenylacyl ethanolamine and choline glycerophospholipids in rabbit platelet membranes

In rabbit platelet membranes, the contents of alkenylacyl phospholipids (plasmalogen) were 56% of phosphatidylethanolamine and 3% of phosphatidylcholine. This uneven distribution of plasmalogens in each phospholipid class could be attributed to the different substrate specificity of ethanolaminephosphotransferase (EC 2.7.8.1) and cholinephosphotransferase (EC 2.7.8.2). The properties of the enzymes were studied, using endogenous diglycerides and CDP-[3H]ethanolamine or CDP-[14C]choline as substrates. The newly formed phospholipids were mainly diacyl and alkenylacyl and only rarely alkylacyl type. The ratios of the labeled alkenylacyl to diacyl type of phospholipids clearly varied with the concentrations of CDP-ethanolamine or CDP-choline. When 1, 10, and 30 microM CDP-[3H]ethanolamine were used, the labeled phospholipids contained 53, 37, and 27% of the alkenylacyl type, respectively. The apparent Km for CDP-ethanolamine to synthesize alkenylacyl and diacyl types were 2.2 and 8.1 microM. On the other hand, when 1, 10, and 30 microM CDP-[14C]choline were used, the labeled lipids contained 10, 17, and 24% alkenylacyl type, respectively. The apparent Km for CDP-choline to synthesize alkenylacyl and diacyl types were 24 and 4.3 microM. Further, the syntheses of diacyl type of phosphatidylethanolamine and the alkenylacyl type of phosphatidylcholine were markedly inhibited by unlabeled CDP-choline and CDP-ethanolamine, respectively. The two enzymes had opposite substrate specificities, and ethanolaminephosphotransferase showed a high preference to plasmalogen synthesis, especially in the presence of CDP-choline.