Enzymatic reaction pathways, mapping

The ultimate objective of an X-ray cryoenzymological study is the mapping of the structures of all kinetically significant species along the reaction pathway. In the case of ribonuclease A this has been largely achieved, as described above. Other enzymatic reactions now await application of the same techniques. Unfortunately, not all crystalline enzymes lend themselves to study by this method. In some cases it may be impossible to find a suitable cryoprotective mother liquor in others, the reaction may occur too rapidly at ordinary temperature. A reaction with Acat of 10 seconds and an activation enthalpy of —6 kcal mol will not be quenched even at — 75°C. The approach we have described in this article can be applied to only a small number of enzymes. Two likely candidates for successors to ribonuclease are the enzymes yeast triosephosphate isomerase and porcine pancreatic elastase. 

Our finding of two pyrimidine biosynthetic enzymes (OMPDC and TS) in P. lophurae suggested that, unlike the duckling host, malaria parasites synthesized pyrimidines de novo from precursors such as C02, glutamine and aspartic acid (Walsh and Sherman, 1968b). Since that time, the enzymatic reactions of the de novo pyrimidine pathway and TS have been demonstrated in a variety of Plasmodium spp. and for P. falciparum (available online at http //sites.huji.ac.il/malaria/maps/pyrimidinemetpath. html last accessed 16 July 2008). 

The Malaria Parasite Metabolic Pathway (MPMP) is a website (http // sites.huji.ac.il/malaria last accessed 16 July 2008) that contains over 120 maps that encompasses not only classical biochemical pathways but next to each entry there is a 48-h clock that depicts stage-dependent transcription of a particular gene in P. falciparum. At the clock s zero hour, merozoites invade and at 12 o clock the 48-h cycle terminates. In the middle of the clock appears the hour of maximal transcript level. Clicking on the clock links to a transcriptomic database (http //malaria. ucsf.edu last accessed 16 July 2008). The enzymes are also linked to the International Union of Biochemistry and Molecular Biology website (http //www.iubmb.org last accessed 16 July 2008) where there is a detailed chemistry of the enzymatic reaction. Unlike other databases MPMP has been developed, curated and updated manually (Ginsburg, 2006). 

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