Effect of the age of tobacco leaves on photosynthesis and photorespiration

Relationships among the activities of enzymes related to photosynthesisand photorespiration, and ¹⁴CO₂ photosynthetic products wereinvestigated with individual tobacco leaves attached to thestalk from the bottom to the top. P-glycolate phosphatase ofthe chloroplasts and glycolate oxidase of the peroxisomes hadtheir maximum activities in the 25th leaf from the dicotyledons.Maximum photorespiration was similarly distributed. The highestratio of serine-¹⁴C to glycine-¹⁴C in the photosynthesates andmaximum glycolate formation were also observed in the 25th leaf.Glutamateglyoxylate aminotransferase, serine hydroxymethyltransferaseand glycine decarboxylase were more active in the upper leaves.RuDP carboxylase had nearly constant activity in all leaves,except for the youngest in which activity decreased. MaximumCO₂ photosynthesis and enzyme activity for the C₄ dicarboxylicacid cycle occurred in the upper, youngest leaf. Distributionof photosynthetic CO² fixation among the leaves did not coincidewith RuDP carboxylase activity. The photosynthetic capacityappeared to be better related to the distribution pattern forenzymes of the C₄ dicarboxylic acid pathway, i.e. PEP carboxylase,pyruvate Pi dikinase and 3-PGA phosphatase in the upper leaves.The results suggest that the C₄ dicarboxylic acid pathway participates,to some extent, in photosynthesis in young leaves of tobacco,a dicotyledonous plant. ¹This work was reported at the Annual Meeting (1970) of theJapanese Plant Physiologists in Kobe. ²The Central Research Institute, Japan Monopoly Corporation1-28-3, Nishishinagawa, Shinagawaku, Tokyo, 141 Japan. (Received November 2, 1972; )     

Regulation by induction of branched-chain 2-oxo acid dehydrogenase complex in clofibrate-fed rat liver.

The activity of branched-chain 2-oxo acid dehydrogenase complex increased 3.0-fold in liver of rats fed on 0.1%(w/w) clofibrate. Immunotitration experiments with antibodies against the constituent enzymes of the complex revealed that this increase resulted mainly from the increased amounts of only two(a decarboxylase and a lipoate acyltransferase) of three components of the complex and that the other component(dihydrolipoamide dehydrogenase) remained unchanged in its content, irrespective of clofibrate administration. The increases of both enzyme components were associated with increases in their mRNA levels which were estimated by in vitro translation with poly(A)+ RNA.     

The genotoxicity of a variety of aniline derivatives in a DNA repair test with primary cultured rat hepatocytes

The genotoxicity of a variety of aniline derivatives was examined by a DNA repair test with rat hepatocytes. Out of 37 aniline derivatives, 6 chemicals, i.e., 2,4,6-trimethylaniline (mesidine), 2,4-xylidine, 3,5-diaminobenzoic acid, 3,4-diaminochlorobenzene, 2-chloro-4-methylaniline and 4-chloro-N-methylaniline, elicited positive DNA repair responses. The results are in agreement with the bacterial mutagenicities with or without norharman of these compounds. Positive compounds of unknown carcinogenicity in the present assay, i.e., 3,5-diaminobenzoic acid, 2-chloro-4-methylaniline and 4-chloro-N-methylaniline are suspected of being potentially carcinogenic.     

Intra-strain biological and epidemiological characterization of plum pox virus

Plum pox virus (PPV) is one of the most important plant viruses causing serious economic losses. Thus far, strain typing based on the definition of 10 monophyletic strains with partially differentiable biological properties has been the sole approach used for epidemiological characterization of PPV. However, elucidating the genetic determinants underlying intra-strain biological variation among populations or isolates remains a relevant but unexamined aspect of the epidemiology of the virus. In this study, based on complete nucleotide sequence information of 210 Japanese and 47 non-Japanese isolates of the PPV-Dideron (D) strain, we identified five positively selected sites in the PPV-D genome. Among them, molecular studies showed that amino acid substitutions at position 2,635 in viral replicase correlate with viral titre and competitiveness at the systemic level, suggesting that amino acid position 2,635 is involved in aphid transmission efficiency and symptom severity. Estimation of ancestral genome sequences indicated that substitutions at amino acid position 2,635 were reversible and peculiar to one of two genetically distinct PPV-D populations in Japan. The reversible amino acid evolution probably contributes to the dissemination of the virus population. This study provides the first genomic insight into the evolutionary epidemiology of PPV based on intra-strain biological variation ascribed to positive selection.     

Secreted Nucleobindin-2 Inhibits 3T3-L1 Adipocyte Differentiation

Nucleobindin-2 is a 420 amino acid EF-hand Ca2+ binding protein that can be further processed to generate an 82 amino terminal peptide termed Nesfatin-1. To examine the function of secreted Nucleobindin-2 in adipocyte differentiation, cultured 3T3-L1 cells were incubated with either 0 or 100 nM of GST, GST-Nucleobindin-2, prior to and during the initiation of adipocyte differentiation. Nucleobindin-2 treatment decreased neutral lipid accumulation (Oil-Red O staining) and expression of several marker genes for adipocyte differentiation (PPARγ, aP2, and adipsin). When Nucleobindin- 2 was constitutively secreted into cultured medium, cAMP content and insulin stimulated CREB phosphorylation were significantly reduced. On the other hand, intracellularly overexpressed Nucleobindin-2 failed to affect cAMP content and CREB phosphorylation. Taken together, these data indicate that secreted Nucleobindin-2 is a suppressor of adipocyte differentiation through inhibition of cAMP production and insulin signal.     

Structural Insights into the Epimerization of β-1,4-Linked Oligosaccharides Catalyzed by Cellobiose 2-Epimerase,the Sole Enzyme Epimerizing Non-anomeric Hydroxyl Groups of Unmodified Sugars

Cellobiose 2-epimerase (CE) reversibly converts d-glucose residues into d-mannose residues at the reducing end of unmodified β1,4-linked oligosaccharides, including β-1,4-mannobiose, cellobiose, and lactose. CE is responsible for conversion of β1,4-mannobiose to 4-O-β-d-mannosyl-d-glucose in mannan metabolism. However, the detailed catalytic mechanism of CE is unclear due to the lack of structural data in complex with ligands. We determined the crystal structures of halothermophile Rhodothermus marinus CE (RmCE) in complex with substrates/products or intermediate analogs, and its apo form. The structures in complex with the substrates/products indicated that the residues in the β5-β6 loop as well as those in the inner six helices form the catalytic site. Trp-322 and Trp-385 interact with reducing and non-reducing end parts of these ligands, respectively, by stacking interactions. The architecture of the catalytic site also provided insights into the mechanism of reversible epimerization. His-259 abstracts the H2 proton of the d-mannose residue at the reducing end, and consistently forms the cis-enediol intermediate by facilitated depolarization of the 2-OH group mediated by hydrogen bonding interaction with His-200. His-390 subsequently donates the proton to the C2 atom of the intermediate to form a d-glucose residue. The reverse reaction is mediated by these three histidines with the inverse roles of acid/base catalysts. The conformation of cellobiitol demonstrated that the deprotonation/reprotonation step is coupled with rotation of the C2-C3 bond of the open form of the ligand. Moreover, it is postulated that His-390 is closely related to ring opening/closure by transferring a proton between the O5 and O1 atoms of the ligand.     

Inhibition of ACh-stimulated exocytosis by NSAIDs in guinea pig antral mucous cells: autocrine regulation of mucin secretion by PGE2

The effects of indomethacin (IDM) and aspirin (ASA) on ACh (10 microM) -stimulated exocytotic events were studied in guinea pig antral mucous cells by using video optical microscopy. IDM or ASA, which inhibits cyclooxygenase (COX), decreased the frequency of ACh-stimulated exocytotic events by 30% or 60%, respectively. The extent of inhibition induced by ASA (60%) decreased by 30% when IDM or arachidonic acid (AA, the substrate of COX) was added. IDM, unlike ASA, appears to induce the accumulation of AA, which enhances the frequency of ACh-stimulated exocytotic events in ASA-treated cells. ONO-8713 (100 microM; an inhibitor of the EP1-EP4 prostaglandin receptors) and N-[2-((p-bromocinnamyl)amino)ethyl]-5-isoquinolinesulfonamide, HCl (H-89, 20 microM; an inhibitor of PKA) also decreased the frequency of ACh-stimulated exocytotic events by 60%. However, the supplementation of PGE(2) (1 microM) prevented the IDM-induced decrease in the frequency of ACh-stimulated exocytotic events. SC-560 (an inhibitor of COX-1) decreased the frequency of ACh-stimulated exocytotic events by 30%, but NS-398 (an inhibitor of COX-2) did not. Moreover, IDM decreased the frequency of exocytotic events stimulated by ionomycin, suggesting that COX-1 activity is stimulated by an increase in intracellular Ca(2+) concentration ([Ca(2+)](i)). ACh and ionomycin increased PGE(2) release in antral mucosal cells. In conclusion, in ACh-stimulated antral mucous cells, an increase in [Ca(2+)](i) activates Ca(2+)-regulated exocytotic events and PGE(2) release mediated by COX-1. The released PGE(2) induces the accumulation of cAMP, which enhances the Ca(2+)-regulated exocytosis. The autocrine mechanism mediated by PGE(2) maintains the high-level mucin release from antral mucous cells during ACh stimulation.     

Distribution of a novel protein AgK114 expression in the normal tissues of adult mice: dual expression of AgK114 and growth hormone in anterior pituitary cells

The novel antigen K114 (AgK114) has been previously identified in normal hamster skin, and its expression has been up-regulated accompanying tissue damages of the skin, although there is no information on its biological functions. To determine the physiological role of AgK114, we prepared anti-mouse AgK114 monoclonal antibody and studied its tissue distribution in healthy adult mice by immunocytochemistry. A widespread and unique expression of AgK114 peptide was found in the selected organs of various systems (hair follicle cells and sebaceous gland of skin, ciliated epithelial cells of trachea and bronchial tube, striated portion of submandibular gland, distal convoluted tubule cells of kidney, ciliated epithelial cells of oviduct, medulla of adrenal gland and anterior lobe of pituitary gland). Interestingly, dual expression of AgK114 peptide and growth hormone in somatotrophs was found in anterior lobe of pituitary gland by double immunocytochemistry. AgK114 peptide was expressed widely in many regionally well-defined cellular systems in various peripheral tissues, suggesting that AgK114 peptide may have some roles of physiological functions in these organs. The data from our current study have provided a rationale for further studies of functional roles of AgK114 peptide in a variety of organs or tissues under physiological conditions.     

Involvement of inositol 1,4,5-trisphosphate in Ca2+ influx in thrombin stimulated human platelets

By incubating platelets at low temperature (10 degrees C), the relationship between Ca2+ mobilization and formation of inositol 1,4,5-trisphosphate (IP3) in thrombin stimulated platelets could be precisely investigated. In the presence of 1 mM EGTA, time dependent changes in the intracellular free calcium concentration [( Ca2+]i) were closely related to those in IP3 formation. Time course of the influx of external Ca2+, estimated by delta [Ca2+]i obtained by subtracting [Ca2+]i in the presence of 1 mM EGTA from that in the presence of 1 mM CaCl2 was also very similar to that of IP3 formed. Furthermore, the increase in delta [Ca2+]i was extremely well correlated with the amount of IP3 formed (Y = 49X - 34, r = 0.99). Thus, these data indicate that IP3 might be involved not only in intracellular Ca2+ mobilization but in Ca2+ influx of human platelets stimulated by thrombin.