Plasma adiponectin levels in women with anorexia nervosa.

Adiponectin is a plasma protein exclusively secreted by adipose tissue, which plays a role in modulating lipid and glucose metabolism. The plasma adiponectin concentration shows an inverse correlation with the body mass index in normal and obese individuals, but it has not been investigated in subjects with an extremely low body weight and undernutrition such as anorexia nervosa patients. We investigated plasma adiponectin levels in 21 females with anorexia nervosa. Nineteen healthy females served as the lean control group. The subjects with anorexia nervosa had a significantly lower weight and showed a tendency towards higher adiponectin levels than the control group. No correlation between adiponectin and BMI was found in patients with anorexia nervosa, while a linear negative correlation was seen in lean controls. The patient who showed the lowest adiponectin level reached a life-threatening state and required intravenous feeding in hospital. In association with improved nutrition and weight gain, the adiponectin level increased gradually until the body mass index was about 16 and then decreased subsequently as would be expected in lean normal subjects. These observations suggest that adipose tissue secretes less adiponectin and the adiponectin levels do not show an inverse correlation simply with body mass index in some subjects with severe undernutrition.     

N‐ and C‐terminal peptide sequences are essential for enzyme assembly, allosteric, and/or catalytic properties of ADP‐glucose pyrophosphorylase

ADP-glucose pyrophosphorylase is a key regulatory enzyme in starch synthesis in most plant tissues. Unlike the allosteric regulatory dependent properties of the leaf enzyme, the enzymes from non-photosynthetic tissues exhibit varying levels of sensitivity to allosteric regulation, a behavior which may be an inherent property of the enzyme or a product of post-translational modification. As partial proteolysis of the holoenzyme may account for the wide variation of allosteric regulatory behavior exhibited by enzymes from non-photosynthetic tissues, small N- and C-terminal peptide deletions were made on either the potato large and small subunit and co-expressed with the counterpart wild-type subunit in Escherichia coli. Removal of the putative carboxy-terminal allosteric binding region from either subunit type results in an abolishment of enzyme formation indicating that the carboxy terminus of each subunit type is essential for proper subunit folding and/or enzyme assembly as well as its suggested role in allosteric regulation. Removal of a small 10 amino acid peptide from the N-terminus of the small subunit increased its resistance to the allosteric inhibitor Pi as well as its sensitivity to heat treatment. Likewise, removal of the corresponding peptide (17 residues) at the N-terminus of the large subunit also increased its resistance towards Pi inhibition but, in addition, increased its sensitivity to 3-PGA activation. Deletion of an additional 11 residues reversed these changes in allosteric properties but at the expense of a reduced catalytic turnover rate. Combined, these results indicate that the N- and C-terminal regions are essential for the proper catalytic and allosteric regulatory properties of the potato ADP-glucose pyrophosphorylase. The possible significance of these results on the observed insensitivity to effector molecules by ADP-glucose pyrophosphorylases from other non-photosynthetic tissues is discussed.     

Characterization of RNA binding protein RBP-P reveals a possible role in rice glutelin gene expression and RNA localization

RNA binding proteins (RBPs) play an important role in mRNA metabolism including synthesis, maturation, transport, localization, and stability. In developing rice seeds, RNAs that code for the major storage proteins are transported to specific domains of the cortical endoplasmic reticulum (ER) by a regulated mechanism requiring RNA cis-localization elements, or zipcodes. Putative trans-acting RBPs that recognize prolamine RNA zipcodes required for restricted localization to protein body-ER have previously been identified. Here, we describe the identification of RBP-P using a Northwestern blot approach as an RBP that recognizes and binds to glutelin zipcode RNA, which is required for proper RNA localization to cisternal-ER. RBP-P protein expression coincides with that of glutelin during seed maturation and is localized to both the nucleus and cytosol. RNA-immunoprecipitation and subsequent RT-PCR analysis further demonstrated that RBP-P interacts with glutelin RNAs. In vitro RNA–protein UV-crosslinking assays showed that recombinant RBP-P binds strongly to glutelin mRNA, and in particular, 3′ UTR and zipcode RNA. RBP-P also exhibited strong binding activity to a glutelin intron sequence, suggesting that RBP-P might participate in mRNA splicing. Overall, these results support a multifunctional role for RBP-P in glutelin mRNA metabolism, perhaps in nuclear pre-mRNA splicing and cytosolic localization to the cisternal-ER.     

Association of the positive inotropic action of ouabain with a second species of digitalis receptors

Studies were conducted to determine whether Na-K ATPase or a second species of digitalis receptors in canine cardiac sarcolemma membrane preparations is associated with the positive inotropic action of nontoxic concentrations of ouabain. [3H]ouabain association and dissociation experiments using highly enriched sarcolemma preparations from canine ventricle indicate the presence of two species of ouabain binding receptors. Ouabain binding to Na-K ATPase of the sarcolemma preparation requires supporting ligands and is characterized by fast association and very slow dissociation in vitro. The second species of digitalis receptor does not require supporting ligands for ouabain binding and is characterized by slow association and fast dissociation. To determine which species of digitalis receptor is associated with the positive inotropic action of digitalis, ouabain washout experiments were conducted using various isolated canine myocardial preparations. Washout of the positive inotropic effects of 1.2-2.4 X 10(-7) M ouabain gave half-life values of 1.5-2.0 h for the various myocardial preparations. [3H]ouabain dissociation from the second species of digitalis receptors gave half-life values of 1.7-1.8 h, whereas dissociation from the sarcolemma Na-K ATPase gave half-life values of 8.9-9.3 h for the various sarcolemma preparations utilized. Therefore, based on similarities in half-life values between ouabain inotropy and [3H]ouabain dissociation from the second class of digitalis receptors, it is postulated that the positive inotropic action of digitalis glycosides is associated with the second species of digitalis receptors in the sarcolemma and not with the digitalis inhibitory receptor of Na-K ATPase for nontoxic concentrations of digitalis.     

Accumulation of Prolamines and Glutelins during Rice Seed Development: a Quantitative Evaluation

The levels of prolamines and glutelins, the storage proteinsof rice, were quantified during seed development by immunoblotanalysis. Although both storage proteins were first detectedin 10 day old seeds and their amounts steadily increased throughoutseed development, the relative proportions of glutelins andprolamines were not constant. The molar ratio of glutelins toprolamines was 1.7 in 10 day old seeds and this ratio steadilydecreased to 1.2 in 25 day old seeds due to the increased synthesisand accumulation of prolamines specifically during the latterstages of seed development. In vivo pulse chase labelling studiesconfirmed that the rate of prolamine synthesis as compared tothat evident for glutelin increased during the latter half ofseed development and that protein turnover was not the basisfor the differences in accumulation patterns of these storageproteins. These results indicate that the storage proteins exhibitdifferent temporal accumulation patterns during seed developmentand, moreover, demonstrate that prolamines comprise a much largerproportion of the total storage protein fraction than previouslyrecognized. (Received August 31, 1992; Accepted November 27, 1992)     

Diacylglycerol metabolism and arachidonic acid release in human fetal membranes and decidua vera

Diacylglycerol lipase activity has been demonstrated in human fetal membranes and decidua vera tissues. The specific activity of the enzyme is highest in the microsomal fraction of decidua vera tissue. The acylester bond at the sn-1 position of 1,2-diacyl-sn-glycerol is hydrolyzed followed by release of the fatty acid at the sn-2 position. The diacylglycerol lipase activity present in the microsomal fraction of decidua vera tissue hydrolyzes preferentially a diacylglycerol containing an arachidonoyl group in the sn-2 position. Monoacylglycerol lipase activity was also demonstrated in these tissues. The specific activity of monoacylglycerol lipase was significantly greater than that of diacylglycerol lipase and catalyzed preferentially the hydrolysis of monoacylglycerols containing an arachidonyl group in the sn-2 position. Based on the subcellular distribution and the differential effects of various inhibitors, we suggest that the monoacylglycerol lipase and diacylglycerol lipase in decidua vera tissue are 2 distinct enzymes. Diacylglycerol kinase specific activity was examined also and was found to be 4-5 times greater in amnion than in either chorion laeve or decidua vera. The importance of diacylglycerol metabolism in the mechanism of arachidonic acid release and prostaglandin biosynthesis is discussed.