Development of a kinetic metabolic model: application to Catharanthus roseus hairy root

A kinetic metabolic model describing Catharanthus roseus hairy root growth and nutrition was developed. The metabolic network includes glycolysis, pentose-phosphate pathway, TCA cycle and the catabolic reactions leading to cell building blocks such as amino acids, organic acids, organic phosphates, lipids and structural hexoses. The central primary metabolic network was taken at pseudo-steady state and metabolic flux analysis technique allowed reducing from 31 metabolic fluxes to 20 independent pathways. Hairy root specific growth rate was described as a function of intracellular concentration in cell building blocks. Intracellular transport and accumulation kinetics for major nutrients were included. The model uses intracellular nutrients as well as energy shuttles to describe metabolic regulation. Model calibration was performed using experimental data obtained from batch and medium exchange liquid cultures of C. roseus hairy root using a minimal medium in Petri dish. The model is efficient in estimating the growth rate

Investigations into the molecular size and shape of tomato extensin.

The molecular characteristics of soluble extensin from tomato have been investigated. An apparent molecular mass greater than 240 kDa has been previously observed with the shape-dependent method of gel-filtration chromatography [Brownleader and Dey (1993) Planta (Berlin) 191, 457-469]. Tomato extensin is a heavily glycosylated protein that does not migrate into SDS/polyacrylamide gels. This shape-dependent behaviour raises doubts about agreement between the observed apparent mass and the absolute value. The molecular mass measured with matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF MS) was 72.3 kDa, with no evidence of any other species except a doubly charged ion. The sample was therefore considered to be monodisperse under the conditions used. Electron microscopy of soluble extensin showed the presence of particles 40-50 nm in length and 2.0-2.5 nm in width. A minority of these particles showed a central 'kink'. A number of smaller and generally wider particles (20 nm x 2-4 nm) were considered to be folded monomers and larger particles were thought to be dimers. Sedimentation analysis showed that extensin exists in a rapid monomer-dimer equilibrium in the concentration range and buffer used. Sedimentation equilibrium data gave a Kd of 8.5 microM and sedimentation velocity data generated a Kd between 1 and 10 microM. The concentration dependence of the measured sedimentation coefficient was used, together with hydrodynamic bead modelling, to define plausible shapes for monomer and dimer. This suggests that monomeric extensin is an elongated rod of length 40 nm and width 2 nm, which forms staggered dimers of average length 50 nm and width 3 nm. Extensin is an integral component of the primary cell wall. The physical characteristics (size, shape and form) of the rod-like extensin have been evaluated in this paper so that the role that extensin plays in primary cell wall architecture and during plant disease resistance can be more fully understood

Na+, K+-ATPase isozyme diversity; Comparative biochemistry and physiological implications of novel functional interactions

Na+, K+-ATPase is ubiquitously expressed in the plasma membrane of all animal cells where it serves as the principal regulator of intracellular ion homeostasis. Na+, K+-ATPase is responsible for generating and maintaining transmembrane ionic gradients that are of vital importance for cellular function and subservient activities such as volume regulation, pH maintenance, and generation of action potentials and secondary active transport. The diversity of Na+, K+-ATPase subunit isoforms and their complex spatial and temporal patterns of cellular expression suggest that Na+, K+-ATPase isozymes perform specialized physiological functions. Recent studies have shown that the alpha subunit isoforms possess considerably different kinetic properties and modes of regulation and the beta subunit isoforms modulate the activity, expression and plasma membrane targeting of Na+, K+-ATPase isozymes. This review focuses on recent developments in Na+, K+-ATPase research, and in particular reports of expression of isoforms in various tissues and experiments aimed at elucidating the intrinsic structural features of isoforms important for Na+, K+-ATPase function