Judul: Biosensor antioksidan berbasis superoksida dismutase deinoccus radiodurans diimobilisasi pada nanokomposit zeolit alam indonesia
Abstrak: The immobilization superoxide dismutase extract from D. radioduras on a zeolite nanocomposite modified electrode were studied. Cyclic voltammetry (CV) are employed to investigate the catalytic behavior of the biosensor. The superoxide radical was produced in solution using the xantine/xanthine oksidase system. Antioxidant activity vitamin C was determined by 2, 2-diphenil-2-picrylhydrazyl (DPPH) free radical scavenging method and comparing with biosensor SOD. Optimum conditions for SOD activity was at pH 9, temperature 300 C, zeolite 137.5mg, and SOD 3 U/ml for pure SOD and 9, temperature 300 C, zeolite 137.5mg, and SOD 1500μg/mL for D. radiodurans SOD. Dismutation reaction kinetics of superoxide catalyzed by SOD followed the Lineweaver-Burk kinetics with D. radiodurans SOD Kmapp value was higher than pure SOD. Antioxidant capacity for Vitamin C was 19.49 ppm using DPPH method and value 0,7 for relative antioxidant capacity using biosensor SOD. In conclusion, D radiodurans SOD immobilized on a zeolite nanocomposite had a great potential as biological recognition component for antioxidant biosensor.
Keyword: 

Judul: Aktivitas dan Stabilitas Superoksida Dismutase dari Ekstrak Deinococcus radiodurans yang Diimobilisasi pada Zeolit Alam sebagai Biosensor Antioksidan
Abstrak: Immobilization of superoxide dismutase (SOD) from extract of Deinococcus radiodurans have been studied. D. radiodurans is a bacteria having an enzyme Mn-SOD. The optimum condition of SOD antioxidant activity of the extract was at 31 °C, pH 9, and 157 mg zeolite. Determination of Michaelis-Menten constant was based on Lineweaver- Burk, Eadie-Hoofstee, and Hanes methods. The KMapp of SOD of the extract immobilized on zeolite was lower than that of without immobillization. Electrode stability was relatively stable up to 22 hours. Antioxidant activity of using zeolite as the matrix was higher than that of the unimmobilization. The antioxidant activity on electrode with zeolite at 22nd hour was 64.0 %, and the stability of electrodes without zeolite at the same time was only 49.3 %. The SOD of D. radiodurans is potential as a biosensor for antioxidants because of the high antioxidant activity despite of the low stability.
Keyword: superoxide dismutase, natural zeolites, Deinococcus radiodurans, antioxidant biosensor

Judul: Bifurkasi Hopf pada siklus bisnis IS-LM tanpa dan dengan waktu tunda
Abstrak: One of business cycle models in dynamical economics is the IS-LM business cycle model with time delay, where the time delay lies in stock capital variables. It is a time delay between the existence of stock capital and the time to get ready to invest. In a model without time delay, changing the parameter of investment rate on income could affect the system stability. On the other hand, in a model with time delay, there exists critical time delay changing the system stability. This shows limit cycle, which can be concluded that Hopf bifurcation occurs
Keyword: Bogor Agricultural University (IPB), time delay, Hopf bifurcation, business cycle model