Oxygen consumption in organs of rats treated with serotonin

The serotonin injected intraperitoneally in rats (20 mg/Kg of body weight) increases the oxygen utilization of slices of heart, liver and muscle with a maximum value after 60 min from the injection. The serotonin, probably, acts on intracellular metabolism increasing some enzymatic activities or metabolic pathways.     

Me2+-(13 S) ATPase from Micrococcus sp. ATCC 398E. The effect of trypsin on the purified enzyme.

By trypsin treatment of highly purified ATPase (EC 3.6.1.3) from Micrococcus sp. ATCC 398E, two enzyme modifications have been obtained. (i) ATPase Ta, which has about the same activity as untreated ATPase. (ii) A protein complex Ti, which lacks ATPase activity, but nevertheless binds ATP as shown by affinity chromatography. Trypsin primarily shortens the alpha-chains of the "native" enzyme to alpha-chains and removes the gamma-subunit, thus yielding ATPase Ta. The formation of the protein complex Ti appears to be due to additional cleavage of one alpha-chain into at least two more fractions.     

Kinetic studies on bacterial plasma membrane ATPase (F1). Nucleotide-induced long term inactivation of ATP hydrolyzing activity is linked to the formation of multiple "tight" enzyme nucleotide complexes.

ADP and the ATP analogs Nb-S6ITP (6-[(3-carboxy-4-nitrophenyl)thio]-9-beta-D-ribofuranosylpurine 5'-triphosphate) and AMP-P(NH)P (adenyl-5'-yl imidodiphosphate) interact with soluble plasma membrane ATPase (F1) from Micrococcus species in two ways: (i) at short incubation times, these inhibitors exhibit the kinetics of competitive inhibition, (ii) at long incubation times, these inhibitors induce an inactivation of the ATPase which can be reversed only in the case of AMP-P(NH)P. Kinetic treatment of the long term inactivation by ADP or Nb-S6ITP reveals a pseudo-first order process via the formation of an enzyme-inhibitor complex for which a Km analogous constant is obtained that is identical with the corresponding Ki value of the competitive inhibition. The long term inactivation by ADP and Nb-S6ITP involves the successive "tight" binding of 6 +/- 1 nucleotides/F1 molecule. One additional ADP molecule/F1 complex which is also "tightly" bound has no effect on the ATPase activity. The long term inactivation by ADP and Nb-S6ITP is inhibited at higher inhibitor concentrations according to a kinetics analogous to a substrate excess inhibition. Evidence is presented indicating that the mechanism of ATP hydrolysis by F1 and the long term inactivation by ADP or Nb-S6ITP are related processes. The mechanism of long term inactivation by AMP-P(NH)P appears to be different from that of ADP or Nb-S6ITP.