Beak and radula growth in Octopus vulgaris

The dry weight and the crest length of the upper and lower beak, the length of the radula ribbon, the average width of the base of the six proximal and distal rachidian teeth as well as the total number of these teeth have all been related to the live body weight of octopuses between 1.1 and 4440 g. From any one of these parameters it is possible to estimate the size and approximate age of the animal.     

Site-directed mutagenesis of the ionizable groups in the active site of Zymomonas mobilis pyruvate decarboxylase: effect on activity and pH dependence.

Pyruvate decarboxylase (PDC, EC 4.1.1.1) is a thiamin diphosphate-dependent enzyme about which there is a large body of structural and functional information. The active site contains several absolutely conserved ionizable groups and all of these appear to be important, as judged by the fact that mutation diminishes or abolishes catalytic activity. Previously we have shown [Schenk, G., Leeper, F.J., England, R., Nixon, P.F. & Duggleby, R.G. (1997) Eur. J. Biochem. 248, 63-71] that the activity is pH-dependent due to changes in kcat/Km while kcat itself is unaffected by pH. The effect on kcat/Km is determined by a group with a pKa of 6.45; the identity of this group has not been determined, although H113 is a possible candidate. Here we mutate five crucial residues in the active site with ionizable side-chains (D27, E50, H113, H114 and E473) in turn, to residues that are nonionizable or should have a substantially altered pKa. Each protein was purified and characterized kinetically. Unexpectedly, the pH-dependence of kcat/Km is largely unaffected in all mutants, ruling out the possibility that any of these five residues is responsible for the observed pKa of 6.45. We conjecture that the kcat/Km profile reflects the protonation of an alcoholate anion intermediate of the catalytic cycle.     

AN AMPLIFICATION OF THE PHYLOGENETIC SPECIES CONCEPT

Abstract— The goal of a phylogenetic species concept is to reveal the smallest units that are analysable by cladistic methods and interpretable as the result of phylogenctic history. We define species as the smallest aggregation of populations (sexual) or lineagcs (asexual) diagnosable by a unique combination of character states in comparable individuals (semaphoronts). A character state is an inherited attribute distributed among all comparable individuals (semaphoronts) of the same historical population, clade, or terminal lineage. This definition of species is character-based and pattern oriented. Evolutionary explanations of phylogenetic species are consistent with contemporary explanations of processes of speciation, but require only the assumption of nested hierarchical pattern. We discuss the compatibility of the phylogenetic species concept with various biological needs for species and justify its use at the exclusion of alternative species concepts.     

The structure and evolution of the spider monkey delta-globin gene

We have isolated the delta-globin gene of the New-World spider monkey, Ateles geoffroyi, and compared its nucleotide sequence with those of other primate delta- and beta-globin genes. Among primate delta-globin genes, the rate of nonsynonymous substitutions is much less than the rate of synonymous substitutions. This suggests that primate delta- globin genes may remain under evolutionary conservation, perhaps because hemoglobin A2 has an as yet unknown physiological importance.      

Slow axonal transport.

New studies provide further evidence that the neuronal cytoskeleton is the product of a dynamic interplay between axonal transport processes and locally regulated assembly mechanisms. These data confirm that the axonal cytoskeleton in mammalian systems is largely stationary and is maintained by a smaller pool of moving subunits or polymers. Slow axonal transport in certain lower species, however, may exhibit quite different features.     

Differential turnover of phosphate groups on neurofilament subunits in mammalian neurons in vivo

The phosphorylation and dephosphorylation of specific proteins was demonstrated directly in the intact vertebrate nervous system in vivo. By exploiting the neurons' ability to segregate a select group of cytoskeletal proteins from most other phosphorylated constituents of the cell by axoplasmic transport, we were able to examine the dynamics of phosphate turnover on neurofilament proteins in mouse retinal ganglion cell neurons simultaneously labeled with [32P]orthophosphate and [3H]proline in vivo. Three [3H]proline-labeled neurofilament protein (NFP) subunits, designated H (160-200 kDa), M (135-145 kDa), and L (68-70 kDa), entered optic axons in a mole:mole ratio similar to that of isolated axonal neurofilaments, supporting the notion that newly synthesized NFPs are transported along axons as assembled neurofilaments. NFP subunits incorporated high levels of 32P before reaching axonal sites at the level of the optic nerve. As neurofilaments were transported along axons, however, many initially incorporated [32P]phosphate groups were removed. Loss of these phosphate groups occurred to a different extent on each subunit. A minimum of 50-60 and 35-40% of the labeled phosphate groups was removed in a 5-day period from the L and M subunits, respectively. By contrast, the H subunit exhibited relatively little or no phosphate turnover during the same period. Dephosphorylation of L in axons is accompanied by a decrease in its net state of phosphorylation; changes in the phosphorylation state of H and M, however, also reflect ongoing addition of phosphates to these polypeptides during axonal transport (Nixon, R.A., Lewis, S.E., and Marotta, C.A. (1986) J. Neurosci., in press). The possibility is raised that dynamic rearrangements of phosphate topography on NFPs represent a mechanism to coordinate interactions of neurofilaments with other proteins as these elements are transported and incorporated into the stationary cytoskeleton along retinal ganglion cell axons.