Mitochondrial NAD(P)-malic enzyme from herring skeletal muscle

Mitochondrial NAD(P)-dependent malic enzyme [EC 1.1.1.39, L-malate: NAD⁺ oxidoreductase (decarboxylating)] was purified from herring skeletal muscle to a specific activity of 8.2 mol/min/mg. The purification procedure involved chromatography on DEAE-cellulose, Red Agarose and a Sephacryl S-300 with a final recovery of 38% of enzyme activity. This enzyme catalyzes the oxidative decarboxylation of malate in the presence of either NAD or NADP in the presence of Mn²⁺. Some kinetic characteristics of this enzyme were determined. The pH optimum of activity is 7.0. ATP was shown to be a competitive inhibitor with malate. The inhibition by ATP displayed hyperbolic competitive kinetics with a K_i (ATP) of 0.28 mM in the presence of NAD and 0.75 mM in the presence of NADP. Fumarate reversed ATP inhibition.In vivo, regulation of NAD(P)-dependent malic enzyme might respond to changing levels of mitochondrial ATP and fumarate with the enzyme undergoing kinetic activation by an increase in the concentration of mitochondrial fumarate which could reverse enzyme inhibition by ATP.     

Mitochondrial NAD(P)-dependent malic enzyme from herring testicular tissue: Purification,kinetic behaviour and regulatory properties

Mitochondrial NAD(P)-dependent malic enzyme [EC 1.1.1.39, L-malate: NAD⁺ oxidoreductase (decarboxylating)] was purified from herring testicular tissue to a specific activity of 26.4 μmol NADH/min/mg protein. Herring testicular tissue is one of the most abundant sources of this enzyme. The purification procedure involved differential centrifugation of mitochondria and then chromatography on DEAE-Sephacel, Red Agarose and Sephacryl S-300. This enzyme catalyzes the oxidative decarboxylation of malate in the presence of Mn²⁺ and either NAD or NADP. Under V_max conditions the ratios for the rate of NAD/NADP reduction was 1.8. A study of the reductive carboxulation reaction indicated that this enzyme reaction is reversible; at pH 7.0 the reverse reaction exhibited 22% of the activity of forward reaction. Some kinetic characteristics of the enzyme were determined. ATP was found to be a competitive inhibitor with respect to malate. Fumarate reversed ATP inhibition. Regulation of NAD(P)-dependent malic enzyme from herring testicular tissue mitochondria could respond to changing levels of mitochondrial ATP and fumarate in vivo.     

Pollutant loadings from solvay waste beds to lower Ninemile Creek,New York

Concentrations of Cl, total ammonia (TNH₃), NO₃ plus NO₂, total P (TP), and soluble reactive P (SRP) were measured at two sites, located 5 km apart, on Ninemile Creek, New York, for a period of more than 8 mo. The sites bound the most recently formed Solvay waste beds, associated with the production of soda ash, that adjoin the creek. Concentrations of Cl and T-NH₃ increased on average by factors of 16.1 and 7.6, respectively, over the monitored stream reach. The estimated average loadings of these materials to the stream over this reach were 2.3 × 10⁵ and 1.2 × 102 kg d^?1, respectively. These inputs are attributable to the Solvay waste beds. The loading of Cl from this source has not changed significantly over a 4 yr period since the closure of the soda ash manufacturing facility. This is the single largest source of Cl, and the second largest source of T-NH₃, to polluted Onondaga Lake. Profiles of Cl in the lake indicated that at times the creek inflow plunges to subsurface layers as a result of its elevated density. This is at least in part a result of the creek's ionic enrichment. The concentration of SRP decreased by a factor of 2.0 on average over the study reach, probably due to adsorption to the CaCO₃ deposits that cover the stream bed in this area. However, the TP load from the creek to the lake is not significantly affected by this phenomenon.     

Timing of hot spot--related volcanism and the breakup of madagascar and India

Widespread basalts and rhyolites were erupted in Madagascar during the Late Cretaceous. These are considered to be related to the Marion hot spot and the breakup of Madagascar and Greater India. Seventeen argon-40/argon-39 age determinations reveal that volcanic rocks and dikes from the 1500-kilometer-long rifted eastern margin of Madagascar were emplaced rapidly (mean age = 87.6 +/- 0.6 million years ago) and that the entire duration of Cretaceous volcanism on the island was no more than 6 million years. The evidence suggests that the thick lava pile at Volcan de l'Androy in the south of the island marks the focal point of the Marion hot spot at approximately 88 million years ago and that this mantle plume was instrumental in causing continental breakup.