In response to changes in nutrient conditions, cells rearrange the composition of plasma membrane (PM) transporters to optimize their metabolic flux. Not only transcriptional gene regulation, but also inactivation of specific transporters is important for fast rearrangement of the PM. In eukaryotic cells, endocytosis plays a role in transporter inactivation, which is triggered by ubiquitination of these transporters. The Nedd4 family E3 ubiquitin ligase is responsible for ubiquitination of the PM transporters and requires that a series of α-arrestin proteins are targeted to these transporters. The mechanism by which an α-arrestin recognizes its cognate transporters in response to environmental signals is of intense scientific interest. Excess substrates or signal transduction pathways are known to initiate recognition of transporters by α-arrestins. Here, we identified an endocytic-sorting signal in the monocarboxylate transporter Jen1 from yeast (), whose endocytic degradation depends on the Snf1-glucose signaling pathway. We found that the C-terminal 20-amino acid-long region of Jen1 contains an amino acid sequence required for association of Jen1 to the α-arrestin Rod1, as well as lysine residues important for glucose-induced Jen1 ubiquitination. Notably, fusion of this region to the methionine permease, Mup1, whose endocytosis is normally induced by excess methionine, was sufficient for Mup1 to undergo glucose-induced, Rod1-mediated endocytosis. Taken together, our results demonstrate that the Jen1 C-terminal region acts as a glucose-responding degron for α-arrestin-mediated endocytic degradation of Jen1.

A large amount of PV penetration may introduce uncertainties in future power system planning and operations. This paper proposes the concept of “Robust Security (RS)” and the “RS region” in order to investigate power system security in the presence of a large amount of uncertainties. The RS region is defined as the region of power system operation where the system is secure under uncertainties. It is shown that the region tends to shrink and disappear for a high degree of PV penetration. Emerging problems concerned with security in future power systems are investigated. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 182(1): 30–38, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22289

SUMMARYMega penetration of photovoltaic power generation (PV) will be introduced in future electric power systems, dealing with environmental problems such as global warming and energy exhaustion. The authors have pointed out that difficulties will arise in meeting the N-1 security standard if increases in uncertainties cannot be avoided due to PV penetration. Thus, we have proposed a new concept of "robust power system security" together with several conditions to be satisfied in order to guarantee the N-1 security standard under uncertainties. In this paper, (1) a model of uncertainties due to PV generation is proposed based on robust power system security; a method for proper parameter selection is also provided. Then, (2) the influence on the stability of the PV and load disconnection from the power system is studied through simulation using the model system; (3) the effect of PV fault ride-through (FRT) on stability is investigated along with dynamic voltage support (DVS). Finally, it is shown that (4) complicated and burdensome tasks will be considerably increased in power system operation planning and real-time operation under future circumstances by the mega penetration of PV.

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Penetration of large amount of renewable energy sources (RES) may introduce considerable uncertainties in power systems making difficult the planning and operation tasks. This paper proposes a new concept named "Robust Power System Security (RS)" in order to investigate power system security in the presence of uncertainties. RS region is defined as an area of power system operation in which the system is secure regardless of uncertainties in parameters such as RES outputs. When the size of the uncertainties is specified, RS region is identified. It is observed that the region tends to shrink and disappear as the uncertainty increases. Emerging problems concerned with security issues in future power systems are investigated.Simulations under large RES penetration are carried out using a three generators test system. Possible applications of the proposed concept toward real-time operation problems are discussed for keeping up the security. Index Terms-RobustPower System Security(RS), Renewable energy sources(RES), Transient stability, Uncertainties. Naoto Yorino (M'90) received the B.S., M.S.