The maximum velocity depends on the concentration of enzyme. If two enzyme preparations are pure, then one can compare the values of the turnover number kcat, which is equal to Vmax/[E]total. One also has to specify the organism from which the enzyme derives.
One place to look for enzyme information is BRENDA. I would probably go there first, but if that is not successful, Pubmed is a useful tool for searching the biochemical literature. There is also an older publication "Biochemica Information" edited by Joseph Keesey and published by Boeringer Mannheim that has some information and tips on this enzyme on pp. 27-28. Methods of Enzymatic Analysis edited by Bergmeyer also has some information.