Background: Some phenolic compounds are potential source for arginase inhibitor that can be used in management of disease associated with endothelial dysfunction. Objective: The aim of this study was to investigate the inhibitory effect on arginase and to determine total phenolic content of extracts from different parts of Melastoma malabathricum L. Methods: Each part were extracted with 70% ethanol by maceration. The extracts were mixed with bovine liver arginase and L-arginine as a substrate. The inhibitory effect of extracts were determined in vitro, by measuring its absorbance on 430 nm. Total phenolic content were determined with Folin-Ciocalteu 25% on 750 nm. Results: The 70% ethanol extract of M. malabathricum leaves at 100 μg/mL was found to have highest inhibition (81.26 ± 5.27 %) followed by flower 73.39 ± 9.39%, fruit 67.63 ± 7.61 and stem 61.61 ± 4.56%. The IC50 value of the most active extract was 62.43 μg/mL while the IC50 value of N-hidroksi-nor-L-arginin (nor-NOHA) acetate, an arginase inhibitor was found to be 3.91 μg/mL. Total phenolic content of 70% ethanolic extracts of M. malabathricum leaves, flower, fruit and stem was 15.9, 20.7, 6.44, and 6.29%. Conclusion: The 70% ethanol extract of M. malabathricum leaves exhibited the highest inhibition on arginase but highest total phenolic content was from flower part. Pearson correlation test showed no correlation p>0.05 between arginase inhibition and total phenolic content of the samples.
Key words: Arginase, L-arginine, Melastoma malabathricum.