Palaeocommunity Dynamics and Behavioral Analysis of Conichnus: Bhuj Formation (Lower Cretaceous),Kachchh-India

A palaeocommunity of large Conichnus conicus, a conical, cone-in-cone shaped burrow, created by sea anemones, occurs in medium-grained, crossbedded, well-sorted sandstone in the middle part of the Cretaceous Guneri Member of the Bhuj Formation in India. The trace fossil Conichnus is considered to be a common element of the Skolithos ichnofacies and is interpreted to reflect equilibrium movement in response to substrate aggradation. In the present study, three different varieties of Conichnus conicus are distinguished based on morphology and internal fabric. Community dynamics and burrowing behavior are revealed by inter-burrow relationships, burrow initiation levels and sedimentology. Three types of behavior are envisaged: retrusive equilibrium, protrusive equilibrium response, and escape behavior. Palaeocommunity dynamics show that the tracemakers consisted of only adult organisms that initiated burrows during neap tides and are adapted to feed effectively during weak flow conditions. The occurrence of Conichnus palaeocommunity in the Guneri Member indicates the tidal conditions in a fully marine setting. Results presented herein may aid in the understanding of palaeocommunity dynamics in other shallow marine sequences.     

The isolation,characterization and application in the Triticeae of a set of wheat RFLP probes identifying each homoeologous chromosome arm

Summary To investigate the use of RFLP analysis in the Triticeae, a set of low copy number probes has been isolated from a wheat cDNA library. The probes identify each of the 14 homoeologous chromosome arms of wheat as determined by analysis of DNA fragments hybridizing to the probes in aneuploid lines of Chinese Spring. These probes can be used in RFLP analyses both for the assignment of homoeology of alien chromosomes or arms added to wheat, and for the determination of chromosome dosage in wheat aneuploids. Different chromosomes from various Triticeae species can therefore be followed in a wheat genetic background using a single technique. The potential uses of the set in facilitating the transfer of alien segments into wheat are outlined.     

Kinetic isotope effect studies on aspartate aminotransferase: evidence for a concerted 1,3 prototropic shift mechanism for the cytoplasmic isozyme and L-aspartate and dichotomy in mechanism

The C alpha primary hydrogen kinetic isotope effects (C alpha-KIEs) for the reaction of the cytoplasmic isozyme of aspartate aminotransferase (cAATase) with [alpha-2H]-L-aspartate are small and only slightly affected by deuterium oxide solvent (DV = 1.43 +/- 0.03 and DV/KAsp = 1.36 +/- 0.04 in H2O; DV = 1.44 +/- 0.01 and DV/KAsp = 1.61 +/- 0.06 in D2O). The D2O solvent KIEs (SKIEs) are somewhat larger and are essentially independent of deuterium at C alpha (D2OV = 2.21 +/- 0.07 and D2OV/KAsp = 1.70 +/- 0.03 with [alpha-1H]-L-aspartate; D2OV = 2.34 +/- 0.12 and D2OV/KAsp = 1.82 +/- 0.06 with [alpha-2H]-L- aspartate). The C alpha-KIEs on V and on V/KAsp are independent of pH from pH 5.0 to pH 10.0. These results support a rate-determining concerted 1,3 prototropic shift mechanism by the multiple KIE criteria [Hermes, J. D., Roeske, C. A., O'Leary, M. H., & Cleland, W. W. (1982) Biochemistry 21, 5106]. The large C alpha-KIEs for the reaction of mitochondrial AATase (mAATase) with L-glutamate (DV = 1.88 +/- 0.13 and DV/KGlu = 3.80 +/- 0.43 in H2O; DV = 1.57 +/- 0.05 and DV/KGlu = 4.21 +/- 0.19 in D2O) coupled with the relatively small SKIEs (D2OV = 1.58 +/- 0.04 and D2OV/KGlu = 1.25 +/- 0.05 with [alpha-1H]-L-glutamate; D2OV = 1.46 +/- 0.06 and D2OV/KGlu = 1.16 +/- 0.05 with [alpha-2H]-L-glutamate) are most consistent with a two-step mechanism for the 1,3 prototropic shift for this isozyme-substrate pair.(ABSTRACT TRUNCATED AT 250 WORDS)     

Aspartate aminotransferase catalyzed oxygen exchange with solvent from oxygen-18-enriched alpha-ketoglutarate: evidence for slow exchange of enzyme-bound water

Partitioning of the ketimine (or ketimine + quinonoid) intermediate(s) in the mitochondrial aspartate aminotransferase reactions was investigated by following the rates of loss of 18O from carbonyl-18O-enriched alpha-ketoglutarate together with the rate of L-glutamate formation. The ratio of these rate constants was found to equal 1 at 10 degrees C, implying that the above intermediate(s) face(s) equal barriers with respect to the forward and reverse reactions. This partition ratio of 1 together with that measured from the alpha-amino acid side of the reaction [Julin, D.A., Wiesinger, H., Toney, M. D., & Kirsch, J.F. (1989) Biochemistry (preceding paper in this issue)] suggests that the rate constant for exchange of alpha-ketoglutarate-derived H2(18)O from the ketimine (or ketimine + quinonoid) form(s) of the enzyme with solvent is comparable with that for kcat.     

PACAP, a VIP-like peptide, in neurons of the esophagus.

The lower esophagus of guinea-pig, cat, sheep and man was analyzed for pituitary adenylate cyclase activating peptide (PACAP), a novel vasoactive intestinal peptide (VIP)-like peptide, using immunocytochemistry and radioimmunoassay. PACAP-immunoreactive nerve fibers were numerous in the longitudinal and circular muscle layers of sheep and man, moderate in numbers in cat, while being few in the esophagus of guinea-pig. A few PACAP-immunoreactive nerve cell bodies and numerous nerve fibers were seen in the myenteric ganglia of the esophagus of cat, sheep and man. In the lower esophagus of cat, sheep and man all PACAP-containing nerve cell bodies and nerve fibers stored VIP. The results of radioimmunoassay of PACAP in extracts of specimens from man were in good agreement with the immunocytochemical findings. High performance liquid chromatography revealed one major peak of PACAP-like immunoreactivity in extracts of human esophagus. We suggest that neuronal PACAP may serve to modulate motor activity and secretion in the lower esophageal sphincter region.     

On the mechanism of pairing of single- and double-stranded DNA molecules by the recA and single-stranded DNA-binding proteins of Escherichia coli

The pairing of single- and double-stranded DNA molecules at homologous sequences promoted by recA and single-stranded DNA-binding proteins of Escherichia coli follows apparent first-order kinetics. The initial rate and first-order rate constant for the reaction are maximal at approximately 1 recA protein/3 and 1 single-stranded DNA-binding protein/8 nucleotides of single-stranded DNA. The initial rate increases with the concentration of duplex DNA; however, the rate constant is independent of duplex DNA concentration. Both the rate constant and extent of reaction increase linearly with increasing length of duplex DNA over the range 366 to 8623 base pairs. In contrast, the rate constant is independent of the size of the circular single-stranded DNA between 6,400 and 10,100 nucleotides. No significant effect on reaction rate is observed when a single-stranded DNA is paired with 477 base pairs of homologous duplex DNA joined to increasing lengths of heterologous DNA (627-2,367 base pairs). Similarly, heterologous T7 DNA has no effect on the rate of pairing. These findings support a mechanism in which a recA protein-single-stranded DNA complex interacts with the duplex DNA to produce an intermediate in which the two DNA molecules are aligned at homologous sequences. Conversion of the intermediate to a paranemic joint then occurs in a rate-determining unimolecular process.     

Possible Involvement of Phage-Like Structures in Antagonism of Cowpea Rhizobia by Rhizobium trifolii

A reduction in the viability of cowpea rhizobia was observed when Rhizobium trifolii IARI and cowpea Rhizobium strain 3824 were inoculated together in soil. The reduction in number of cowpea rhizobia in soil was found to be associated with the reduction in number of nodules per plant and retardation in plant growth. An antimicrobial substance was isolated from R. trifolii which, on electron microscopic investigation, demonstrated the presence of several phage-like structures.