A CDPK type protein kinase is involved in rice SPS light modulation

A protein kinase activity that can phosphorylate and inactivate rice ( Oryza sativa ) sucrose-phosphate synthase (SPS; UDP-glucose: d -fructose-6-phosphate-2-glucosyl transferase, EC 2.4.1.14) was measured in extracts prepared from leaves exposed to light-dark transitions. Enzyme activity present in extracts from dark leaves was about 5-fold higher than the activity in extracts from leaves that had been collected in the light. The protein kinase (named R-SPSK) was purified about 100-fold from dark leaves and its biochemical properties were studied. The micromolar dependence of Ca²⁺ exhibited by R-SPSK, and its response to calmodulin antagonists was similar to the properties associated with members of the plant Calcium-Dependent Protein Kinase (CDPK) family. Two modulators of SPS activity, Pi and Glc-6-P, were examined for an effect on R-SPSK. While Glc-6-P did not affect R-SPSK activity, Pi drastically increased the kinase activity. Taken together, these data provide evidence that SPS may be regulated by a CDPK type protein-kinase whose activity is modulated by light-dark transitions and stimulated by Pi, the negative effector of SPS activity.     

Clerodane diterpenes from Baccharis sagittalis: insect antifeedant activity

Two clerodane-type diterpene glycosides esters, which were studied as peracetyl derivatives, together with the known diterpene marrubiagenine, were isolated from the aerial part of Baccharis sagittalis (Less). Their structures were established by spectroscopic methods. Antifeedant activity toward Tenebrio molitor larvae of the isolated compounds along with six other diterpenes was evaluated and some structure-antifeedant bioactivity relationships are reported.     

ADP-glucose pyrophosphorylase from wheat endosperm. Purification and characterization of an enzyme with novel regulatory properties

ADP-glucose pyrophosphorylase (AGPase; EC 2.7.7.27) was purified and characterized from two wheat (Triticum aestivum L.) tissues: leaf and endosperm. The leaf enzyme, purified over 1,300-fold, was found to be a heterotetramer composed of subunits of 51 and 54 kDa and possessing regulatory properties typical of AGPases from photosynthetic tissues, being mainly regulated by 3-phosphoglycerate (activator; A0.5=0.01 mM) and orthophosphate (inhibitor; I0.5=0.2 mM). Conversely, the enzyme from wheat endosperm was insensitive to activation by 3-phosphoglycerate and other metabolites. It was, however, inhibited by orthophosphate (I0.5=0.7 mM), ADP (I0.5=3.2 mM) and fructose-1,6-bisphosphate (0.5 = 1.5 mM). All of these inhibitory actions were reversed by 3-phosphoglycerate and fructose-6-phosphate. The endosperm enzyme was found to be a heterotetramer composed of subunits of 52 and 53 kDa, which were recognized by antiserum raised to spinach leaf AGPase. The results suggest that wheat endosperm AGPase possesses distinctive regulatory properties that are relevant in vivo.     

Non-phosphorylating glyceraldehyde-3-phosphate dehydrogenase is post-translationally phosphorylated in heterotrophic cells of wheat (Triticum aestivum)

In wheat, non-phosphorylating, NADP-dependent glyceraldehyde-3-phosphate dehydrogenase (GAPN) was found to be encoded by one gene giving rise to a single protein. However, Western blots revealed two different subunits of about 58 and 60 kDa in endosperm and shoots. The latter was attributed to in vivo phosphorylation of shoot GAPN. No modification occurred in leaves, where the enzyme is composed by a single 58 kDa polypeptide. GAPN partially purified from shoots and endosperm was dephosphorylated in vitro with alkaline phosphatase. Phosphorylated GAPN exhibited similar affinity for substrates but a lower V_max compared to the non-phosphorylated enzyme. Results suggest that reversible phosphorylation of GAPN could regulate NADPH production in the cytosol of heterotrophic plant cells.     

Dynamic thermal balance in the leaf-eared mouse: the interplay among ambient temperature,body size,and behavior

Endotherms maintain constant body temperature through physiological and behavioral adjustments. Behavioral thermoregulation is an important factor influencing energy balance. We exposed the leaf-eared mouse, Phyllotis darwini, to temperatures corresponding to its natural thermal range and studied two forms of behavioral thermoregulation: diminishing surface to volume ratio by huddling and heat dissipation by increasing physical contact with the substrate (flattening). We predicted that at low ambient temperatures (T(a)) huddling would be used as a heat conservation mechanism and at high T(a) flattening would be used for heat loss. We simultaneously measured oxygen consumption (VO2) and flattening, in response to three independent factors: huddling, T(a), and body mass. Each experiment was a 6-h VO2 trial where five virgin females were measured at constant T(a). We performed this protocol for two body mass groups, small (ca. 40 g) and large (ca. 70 g), in a metabolic chamber. Treatments were groups with and without the ability to huddle at five different T(a), ranging from 5 degrees to 35 degrees C. A significant interaction between all three factors was found. Huddling and flattening were used as strategies for conserving or dissipating heat, respectively, and the shift between both strategies occurred at the lower limit of thermoneutrality. At T(a) below thermoneutrality, huddling was a more effective way of reducing metabolic requirements and was more efficient (H(E)) in small individuals than large individuals. So, by huddling, small individuals save more energy. At high T(a), flattening appeared to be an equally useful mechanism for heat loss, for both large and small animals.     

Developmental regulation of ENaC subunit mRNA levels in rat kidney

To assess therole of distal nephron apical Na channel (ENaC) gene expression in Nawasting by the immature kidney, ENaC -, -, and -subunit mRNAlevels were examined in the rat by RT-PCR. In microdissected nephronsegments, all three ENaC subunit mRNAs were detected in the distalconvoluted tubule, connecting tubule, cortical collecting duct, andouter medullary collecting duct. The inner medullary collecting ductand all other nephron segments were consistently negative. The mRNAlevels were quantified in kidneys at different developmental stages bymultiplex RT-PCR with "primer dropping," with endoplasmicreticulum-specific cyclophilin mRNA as an internal standard. All threeENaC mRNA levels were low or undetectable on gestationalday 16 and only slightly higher 3 daysbefore birth. A sharp rise was observed between 3 days before and1-3 days after birth; the levels at postnataldays 1-3 were already similar tothose of adult kidneys. The results suggest that ENaC subunit geneexpression is not a limiting factor in the full-term newborn ratkidney, but low levels of expression may limit distal Na absorption inmore immature kidneys, such as those of very premature human infants.