Comparative study of enzyme activities degrading sorbitol, ribitol, xylitol and gluconate in guinea pig tissues

Antiferromagnetic half-skyrmions and bimerons at room temperature

In the quest for post-CMOS (complementary metal-oxide-semiconductor) technologies, driven by the need for improved efficiency and performance, topologically protected ferromagnetic 'whirls' such as skyrmions^1-8 and their anti-particles have shown great promise as solitonic information carriers in racetrack memory-in-logic or neuromorphic devices^1,9-11. However, the presence of dipolar fields in ferromagnets, which restricts the formation of ultrasmall topological textures^3,6,8,9,12, and the deleterious skyrmion Hall effect, when skyrmions are driven by spin torques^9,10,12, have thus far inhibited their practical implementation. Antiferromagnetic analogues, which are predicted to demonstrate relativistic dynamics, fast deflection-free motion and size scaling, have recently become the subject of intense focus^9,13-19, but they have yet to be experimentally demonstrated in natural antiferromagnetic systems. Here we realize a family of topological antiferromagnetic spin textures in α-Fe₂O₃-an Earth-abundant oxide insulator-capped with a platinum overlayer. By exploiting a first-order analogue of the Kibble-Zurek mechanism^20,21, we stabilize exotic merons and antimerons (half-skyrmions)⁸ and their pairs (bimerons)^16,22, which can be erased by magnetic fields and regenerated by temperature cycling. These structures have characteristic sizes of the order of 100 nanometres and can be chemically controlled via precise tuning of the exchange and anisotropy, with pathways through which further scaling may be achieved. Driven by current-based spin torques from the heavy-metal overlayer, some of these antiferromagnetic textures could emerge as prime candidates for low-energy antiferromagnetic spintronics at room temperature^1,9-11,23.

Biochemical characterization of human gluconokinase and the proposed metabolic impact of gluconic acid as determined by constraint based metabolic network analysis

The metabolism of gluconate is well characterized in prokaryotes where it is known to be degraded following phosphorylation by gluconokinase. Less is known of gluconate metabolism in humans. Human gluconokinase activity was recently identified proposing questions about the metabolic role of gluconate in humans. Here we report the recombinant expression, purification and biochemical characterization of isoform I of human gluconokinase alongside substrate specificity and kinetic assays of the enzyme catalyzed reaction. The enzyme, shown to be a dimer, had ATP dependent phosphorylation activity and strict specificity towards gluconate out of 122 substrates tested. In order to evaluate the metabolic impact of gluconate in humans we modeled gluconate metabolism using steady state metabolic network analysis. The results indicate that significant metabolic flux changes in anabolic pathways linked to the hexose monophosphate shunt (HMS) are induced through a small increase in gluconate concentration. We argue that the enzyme takes part in a context specific carbon flux route into the HMS that, in humans, remains incompletely explored. Apart from the biochemical description of human gluconokinase, the results highlight that little is known of the mechanism of gluconate metabolism in humans despite its widespread use in medicine and consumer products.

[Changes in several important metabolic parameters and insulin level during a 7-day total parenteral nutrition under pre- and postoperative conditions]

After the 24 hours preoperative infusion period 0.37% glucose, 0.05% fructose and 1.28% xylitol of the infused amount were excreted in the urine. Postoperatively fructose was the best metabolized energy donator before xylitol and glucose. As a sign of an undisturbed hepatic synthesis of lipoproteins the triglycerides rose up to the 5th postoperative day. During the parenteral nutrition and the additional surgical intervention the cholesterol fell from 192.3 to 128.5 mg/100 ml on the first postoperative day. The infusion solutions caused a rise of the insulin concentration from 23.2 to 46.3 U/l on the operation day. There is a positive nitrogen balance of 3.5 g/24 h on the operation day. The slight negative balance of - 1.15 g/24 h on the first postoperative day is reduced to - 0.61 g/24 h on the postoperative day. The changes of the enzymes LDH, GOT and AP were at normal range. The postoperative changes were due to the surgical intervention. Without a simultaneous change of enzymes, 5 patients had a rise of bilirubin up to 1.1 mg/100 ml. To avoid a too great loose of phosphate during a long-term parenteral nutrition period, it is important to put up a balance.

[Utilization of xylitol in the isolation-perfused myocardium of the rat]

1. In the rat heart muscle, only 3 to 4% of the oxygen-consumption can be referred to xylitol utilization. With xylitol as only substrate the heart is working under substrate deficiency conditions. 2. Diabetes mellitus does not improve the xylitol utilization in the rat heart muscle. 3. The data are compared with the activities of xylitol degrading enzymes in the heart muscle.