chromophore. A picture of ¯uorescent PYP under conditions
of continuous illumination at 100 K is shown in Fig. 3(a).
When the temperature was raised from 100 to 220 K, several
features were observed: (i) a 6.2-fold decrease in ¯uorescence
intensity, (ii) a bathochromic shift of the peak emission
wavelength from 494 to 502 nm, and (iii) the disappearance of
a shoulder at 520 nm.
Fig. 4 shows a ¯uorescence emission spectrum from a crystal
of MalDH in complex with NAD+
/NADH (Dym et al., 1995).
MalDH catalyses the NADH-dependent reduction of oxaloacetate
to malate. The crystal was kept under aerobic condi