Your question is not clear at all. If an enzyme assay is run without the dedicated enzyme then it's not an enzyme assay but an assay to measure the uncatalyzed spontaneous reaction rate. You may run such assay but you have to consider long incubation and/or an effective and sensitive detection method.
May be i understand the question. He is asking for enzyme activity calculation from a source like crude plant extract or bacterial or tissue lysate without using pure enzyme.
Do you mean you want to run a direct assay in which you directly measure product formation (or substrate consumption)? (ie. without using an enzyme coupled assay)...
You can find it in any biochemistry practical book, like look for assay of alkaline or acid phosphatase activity from moong bean seeds or serum. Use the homogenate as enzyme for activity analysis or enzyme units .
I have recently answered about lysozyme assay as follows; i.e.,
I would like to use RP-HPLC enzyme assay using the method of file "Lysozyme by RP-HPLC". It is important to purify by RP-HPLC lysozyme and glyco-lysozyme (at leading peak). I have recently found that glyco-chains in the eucaryotic enzyme is important for the enzyme kinetics (please see file; J Chrom B rat BIN LIP Km). Artificial substrates may be synthesized on your own.
Artificial substrate of Pyridylamination (PA-) of Chitobiose (dimer of β-1,4-linked glucosamine) may be possible to make by Pyridylamination method, which is available from the site
Cellulase assay may be performable using p-nitrophenyl (pNP)-β-D-lactoside or pyridylamination (PA-) of lactose (PA-β-D-lactoside) by measuring liberated aryl-group with an RP-HPLC-photometric or fluorimetric detection.
Xylanase assay may be performable using pNP-Xyl2 by using RP-HPLC. To synthesize the artificial substrate (please see; Kitaoka M.,Haga K.,Kashiwagi Y.,Sasaki T.,Taniguchi H.and Kusakabe I. (1993) Kinetic studies on p-nitrophenyl-cellobioside hydrolyzing xylanase from Cellvibrio gilvus. Biosci.Biotech.Biochem. 57:1987-1989).
Peroxidase assay may be performable by using Spy-LHP (Swallow-tailed perylene derivative for Lipid hydroperoxide) from Wako by using RP-HPLC.
Glutathione peroxidase (GPx) assay may be performable by using reduced glutathione (GSH) as substrate and detection of oxidized glutathione (GSSG) as product by using RP-HPLC (please see again; Lysozyme by RP-HPLC).
In general, when looking for the properties of an enzyme, including assay conditions, the first stop should be the enzyme database BRENDA (http://www.brenda-enzymes.info/)
The assay for peroxidase in plant material is quite simple and hence often performed in student practicals: mix plant juice with hydrogen peroxide and volumetrically determine the rate of O2-formation.