We propose a geometric-morphometrics method (relative warp analysis) to be used in proteomic comparisons. This approach was applied to a dataset from a comparison between 5 controls and 5 patients with colorectal cancer disease published elsewhere. The spots in the 2-D maps were used as landmarks in a morphometric study, and the differences in shape (spot distribution) among them were obtained. The shape variables were used to compare controls and patients. These components mostly ignore random or experimental effects affecting all the proteins in any of the two dimensions studied. Furthermore, the method allows the researcher to find those proteins which contributed the most to the local shape component detected. Applying this approach, we detected variations in the position (isoelectric point and/or relative molecular mass) of some spots that may reflect differences in the amino acidic sequence or post-translational modifications.

Human colon sialidase has been characterized, and its activity levels in normal mucosa and colonic adenocarcinoma have been determined. Sialidase activity was maximal at pH 5.5. and was unstable with storage at 4 and -20 °C. The bulk of activity was pelletassociated. and could not be released with triton X-100 or 3-([3-cholamidopropyl]- dimethylammonio)-l-propanesulfonate. Using 2’-(4-methylumbelliferyl)α-D-N-acelylneuraminic acid as substrate, the K(m) and V(max) values were estimated to be 0.140 mmol/1 and 63 mU/g. respectively. Furthermore, an inhibition by substrate concentrations above 1.5 mmol/1 was detected. Neuraminic acid caused a competitive inhibition with a K(1) of 3.5 mmol/1. A statistically significant increase (p< 0.001) in the sialidase specific activity was found in primary colonic adenocarcinoma (104.20±8.00 mU/g) compared to that of the normal mucosa (72.50±7.67 mU/g).