The effect of temperature (between 5.0 and 45.0°C) on the catalytic activity of nitric oxide synthases types I, II, and III (NOS-I, NOS-II, and NOS-III, respectively) has been investigated, at pH 7.5. The value of V(max) for NOS-I activity increases from 1.8 x 101 pmol min-1 mg-1, at 5.0°C, to 1.8 x 102 pmol min-1 mg-1, at 45.0°C; on the other hand, the value of K(m) (=4.0 x 10-6 M) is temperature independent. Again, the value of V(max) for NOS-II activity increases from 8.0 pmol min-1 mg-1, at 7.0°C, to 5.4 x 101 pmol min-1 mg-1, at 40.0°C, the value of K(m) (=1.8 x 10- 5 M) being unaffected by temperature. Temperature exerts the same effect on NOS-I and NOS-II activity, as shown by the same values of ΔH(V(max)) (=4.2 x 101 kJ mol-1), ΔH(K(m)) (=0 kJ mol-1), and ΔH((V(max)/K(m))) (=4.2 x 101 kJ mol-1). On the contrary, the value of K(m) for NOS-III activity decreases from 3.8 x 10-5 M, at 10.0°C, to 1.6 x 10-5 M, at 40.0°C, the value of V(max) (=6.8 x 101 pmol min-1 mg-1) being temperature independent. Present results indicate that temperature influences directly NOS-I and NOS-II activity independently of the substrate concentration, the values of K(m) being temperature independent. However, when L-arginine level is higher than 2 x 10-4 M, as observed under in vivo conditions, NOS-III activity is essentially unaffected by temperature, the substrate concentration exceeding the value of K(m). As a whole, although further studies in vivo are needed, these observations seem to have potential physiopathologic implications.
- Effect of temperature
- Nitric oxide
- Nitric oxide synthase activity
ASJC Scopus subject areas
- Molecular Biology