Effects of GA3 and IBA on rooting and on the sprouting of buds on stem cuttings of Ipomoea fistulosa

Both IBA and GA₃ enhance rooting, IBA being more effective particularlyat a concentration of 100 mg/liter as compared to 10 mg/liter.IBA decreases while GA₃ increases the sprouting of buds, withboth effects increasing with concentration. GA₃-caused promotionof rooting appears to be due to an increased synthesis of auxinand to an adequate supply of mobilized food materials. ¹ Present address: Department of Biology, University of Missouri,St. Louis, U.S.A. (Received January 26, 1972; )     

Microbial βγ-crystallins

βγ-Crystallins have emerged as a superfamily of structurally homologous proteins with representatives across the domains of life. A major portion of this superfamily is constituted by members from microorganisms. This superfamily has also been recognized as a novel group of Ca²⁺-binding proteins with huge diversity. The βγ domain shows variable properties in Ca²⁺ binding, stability and association with other domains. The various members present a series of evolutionary adaptations culminating in great diversity in properties and functions. Most of the predicted βγ-crystallins are yet to be characterized experimentally. In this review, we outline the distinctive features of microbial βγ-crystallins and their position in the βγ-crystallin superfamily.     

Spectroscopic and viscometric determination of DNA-binding modes of some bioactive dibenzodioxins and phenazines

Push-pull dibenzodioxins and phenazines having ‘anthracene-like’ planar structures and good charge transfer character had been previously synthesised in our laboratory. The dibenzodioxins had earlier proven their anti-proliferative nature against HeLa tumor cell lines. Since phenazines are structural analogues of the former, these molecules were evaluated in course of the current study for their cytotoxic action against HeLa cell lines and they exhibited strong anti-tumor activity. This behavior could be related to their good DNA binding property. The DNA binding modes of molecules 1–4 (Fig. 1) were evaluated using various experimental techniques and they interacted with DNA in a non-covalently by both intercalative as well as groove binding mechanisms. Molecule 1 follows predominantly intercalative binding mode whereas molecules 2 and 3 have nearly equal and opposite preferences for both groove binding and intercalative modes. For molecule 4, groove binding is preferred mode of binding to DNA. A rationale for such differential binding behaviour is provided based on the subtle structural differences in our synthesised dibenzodioxins and phenazines. Elucidation of the mode of a molecule-DNA-binding event is relevant for understanding the mechanism of action of these molecules and will help promote further research into designing better DNA targeting small molecules.     

Exploring the role of cation-pi interactions in glycoproteins lipid-binding proteins and RNA-binding proteins

We have analyzed and compared the influence of cation-pi interactions in glycoproteins (GPs), lipid-binding proteins (LBPs) and RNA-binding proteins (RBPs) in this study. We observed that all the proteins included in the study had profound cation-pi interactions. There is an average of one energetically significant cation-pi interaction for every 71 residues in GPs, for every 58 residues in LBPs and for every 64 residues in RBPs. Long-range contacts are predominant in all the three types of proteins studied. The pair-wise cation-pi interaction energy between the positively charged and aromatic residues shows that Arg-Trp pair energy was the strongest among all six possible pairs in all the three types of proteins studied. There were considerable differences in the preference of cation-pi interacting residues to different secondary structure elements and ASA and these might contribute to differences in biochemical functions of GPs, LBPs and RBPs. It was interesting to note that all the five residues involved in cation-pi interactions were found to have stabilization centers in GPs, LBPs and RBPs. Majority of the cation-pi interacting residues investigated in the present study had a conservation score of 6, the cutoff value used to identify the stabilizing residues. A small percentage of cation-pi interacting residues were also present as stabilizing residues. The cation-pi interaction-forming residues play an important role in the structural stability of in GPs, LBPs and RBPs. The results obtained in this study will be helpful in further understanding the stability, specificity and differences in the biochemical functions of GPs, LBPs and RBPs.     

Biotransformation of aromatic and heterocyclic amides by amidase of whole cells of Rhodococcus sp. MTB5: Biocatalytic characterization and substrate specificity

In this study, an amidohydrolase activity of amidase in whole cells of Rhodococcus sp. MTB5 has been used for the biotransformation of aromatic, monoheterocyclic and diheterocyclic amides to corresponding carboxylic acids. Benzoic acid, nicotinic acid and pyrazinoic acid are carboxylic acids which have wide industrial applications. The amidase of this strain is found to be inducible in nature. The biocatalytic conditions for amidase present in the whole cells of MTB5 were optimized against benzamide. The enzyme exhibited optimum activity in 50?mM potassium phosphate buffer pH 7.0. The optimum temperature and substrate concentrations for this enzyme were 50?°C and 50?mM, respectively. The enzyme was quite stable for more than 6?h at 30?°C. It showed substrate specificity against different amides, including aliphatic, aromatic and heterocyclic amides. Under optimized reaction conditions, the amidase is capable of converting 50?mM each of benzamide, nicotinamide and pyrazinamide to corresponding acids within 100, 160 and 120?min, respectively, using 5?mg dry cell mass (DCM) per mL of reaction mixture. The respective percent conversion of these amides was 95.02%, 98.00% and 98.44% achieved by whole cells. The amidase in whole cells can withstand as high as 383?mM concentration of product in a reaction mixture and above which it undergoes product feedback inhibition. The results of this study suggest that Rhodococcus sp. MTB5 amidase has the potential for large-scale production of carboxylic acids of industrial value.     

Role of phenylalanine B10 in plant nonsymbiotic hemoglobins

All plants contain an unusual class of hemoglobins that display bis-histidyl coordination yet are able to bind exogenous ligands such as oxygen. Structurally homologous hexacoordinate hemoglobins (hxHbs) are also found in animals (neuroglobin and cytoglobin) and some cyanobacteria, where they are thought to play a role in free radical scavenging or ligand sensing. The plant hxHbs can be distinguished from the others because they are only weakly hexcacoordinate in the ferrous state, yet no structural mechanism for regulating hexacoordination has been articulated to account for this behavior. Plant hxHbs contain a conserved Phe at position B10 (Phe(B10)), which is near the reversibly coordinated distal His(E7). We have investigated the effects of Phe(B10) mutation on kinetic and equilibrium constants for hexacoordination and exogenous ligand binding in the ferrous and ferric oxidation states. Kinetic and equilibrium constants for hexacoordination and ligand binding along with CO-FTIR spectroscopy, midpoint reduction potentials, and the crystal structures of two key mutant proteins (F40W and F40L) reveal that Phe(B10) is an important regulatory element in hexacoordination. We show that Phe at this position is the only amino acid that facilitates stable oxygen binding to the ferrous Hb and the only one that promotes ligand binding in the ferric oxidation states. This work presents a structural mechanism for regulating reversible intramolecular coordination in plant hxHbs.     

A role for apolipoprotein(a) in protection of the low-density lipoprotein component of lipoprotein(a) from copper-mediated oxidation

Low-density lipoprotein (LDL) oxidation is stimulated by copper. Addition of a recombinant form of apolipoprotein(a) (apo(a); the distinguishing protein component of lipoprotein(a)) containing 17 plasminogen kringle IV-like domains (17K r-apo(a)) protects LDL against oxidation by copper. Protection is specific to apo(a) and is not achieved by plasminogen or serum albumin. When Cu(2+) is added to 17K r-apo(a), its intrinsic fluorescence is quenched in a concentration-dependent and saturable manner. Quenching is unchanged whether performed aerobically or anaerobically and is reversible by ethylenediaminetetraacetate, suggesting that it is due to equilibrium binding of Cu(2+) and not to oxidative destruction of tryptophan residues. The fluorescence change exhibits a sigmoid dependence on copper concentration, and time courses of quenching are complex. At copper concentrations below 10 microM there is little quenching, whereas above 10 microM quenching proceeds immediately as a double-exponential decay. The affinity and kinetics of copper binding to 17K r-apo(a) are diminished in the presence of the lysine analogue epsilon -aminocaproic acid. We propose that copper binding to the kringle domains of 17K is mediated by a His-X-His sequence that is located about 5A from the closest tryptophan residue of the lysine binding pocket. Copper binding may account for the natural resistance to copper-mediated oxidation of lipoprotein(a) relative to LDL that has been previously reported and for the protection afforded by apo(a) from copper-mediated oxidation of LDL that we describe in the present study.