Alkaline Phosphatases: Structure, substrate specificity and functional relatedness to other members of a large superfamily of enzymes

Our knowledge of the structure and function of alkaline phosphatases has increased greatly in recent years. The crystal structure of the human placental isozyme has enabled us to probe salient features of the mammalian enzymes that differ from those of the bacterial enzymes. The availability of knockout mice deficient in each of the murine alkaline phosphatase isozymes has also given deep insights into their in vivo role. This has been particularly true for probing the biological role of bone alkaline phosphatase during skeletal mineralization. Due to space constraints this mini-review focuses exclusively on structural and functional features of mammalian alkaline phosphatases as identified by crystallography and probed by site-directed mutagenesis and kinetic analysis. An emphasis is also placed on the substrate specificity of alkaline phosphatases, their catalytic properties as phosphohydrolases as well as phosphodiesterases and their structural and functional relatedness to a large superfamily of enzymes that includes nucleotide pyrophosphatase/phosphodiesterase

Bone Mechanical Properties Estimation with the Cell Method

2D Bone Mechanical Properties Estimation with the Cell Metho

Applicazione del Metodo delle Celle alla simulazione del comportamento meccanico dell\u2019osso trabecolare

Al crescere dell\u2019et\ue0 media della popolazione, \ue8 andata aumentando l\u2019importanza dell\u2019osteoporosi come problema di salute pubblica. Nella valutazione del rischio di frattura, non \ue8 possibile determinare resistenza e propriet\ue0 elastiche dell\u2019osso sulla base soltanto di composizione e densit\ue0, ma un ruolo determinante \ue8 svolto dall\u2019architettura assunta dalla struttura ossea. La moderna tecnologia permette accurate acquisizioni volumetriche di porzioni di osso trabecolare, ma la modellazione e l\u2019analisi numerica basate sul FEM presentano degli inconvenienti che ne limitano in pratica l\u2019utilizzo. Il Metodo delle Celle, particolarmente adatto in presenza di eterogeneit\ue0 o di discontinuit\ue0, permette di superare gli inconvenienti incontrati con una modellazione agli Elementi Finiti. Scopo di questo lavoro \ue8 presentare alcuni risultati preliminari ottenuti nella stima del modulo elastico di espianti di osso trabecolare mediante una particolare applicazione del Metodo delle Celle, a partire da immagini di micro-CT con radiazione di sincrotrone presso la beamline SYRMEP di Elettra (Trieste)

Membrane stretch activates a potassium channel in pig articular chondrocytes

BIOCHIMICA BIOPHYSICA ACT

Dual mechanism for cAMP-dependent modulation of Ca2+ signalling in articular chondrocytes.

The ability of cAMP to modulate the actions of Ca(2+)-mobilizing agonists was studied in single Fura-2-loaded pig articular chondrocytes in primary culture. Forskolin and 8-Br-cAMP increased both the frequency and amplitude of Ca2+ oscillations induced by ATP, and, in unstimulated cells, induced single Ca2+ transients or even Ca2+ oscillations. The cAMP-dependent protein kinase inhibitor H89 totally prevented the effect of cAMP-elevating agents on Ca2+ signalling. Forskolin and 8-Br-cAMP promptly increased the rate of Mn2+ quenching, when administered in the presence of ATP, suggesting a potentiation of receptor-mediated Ca2+ influx. In Ca(2+)-free medium, ATP-induced Ca2+ oscillations decreased and stopped after a few cycles: subsequent ATP additions temporarily resumed the activity, an effect that could be mimicked by forskolin. The same agent induced single Ca2+ transients in 42% of the cell population maintained in Ca(2+)-free medium. Thapsigargin prevented Ca2+ responses to both ATP and forskolin. The results indicate a dual mechanism for cAMP-induced potentiation of Ca2+ signalling in articular chondrocytes: an increase of receptor-mediated Ca2+ influx and a positive modulation of intracellular Ca2+ release

Dual mechanism for c-AMP-dependent modulation of Ca2+-signalling in articular chondrocytes

BIOCHEMICAL J