Yaw Huei Lin

Dioscorins, the major tuber storage proteins of yam (Dioscorea batatas Decne), with dehydroascorbate reductase and monodehydroascorbate reductase activities

Dioscorins, the major storage proteins of yam (Dioscorea batatas Decne), were purified from the tubers according to the methods of Hou et al. (W.C. Hou, J.S. Liu, H.J. Chen, T.E. Chen, C.F. Chang, Y.H. Lin, Dioscorin, the major tuber storage protein of yam (Dioscorea batatas Decne), with carbonic anhydrase and trypsin inhibitor activities, J. Agric. Food Chem. 47 (1999) 2168‐2172.). Dioscorins reduced dehydroascorbate (DHA) in the presence of glutathione to regenerate ascorbate (AsA). However, without glutathione, dioscorins has very low DHA reductase activity. Intermolecular thiol‐disulfide interchanges of dioscorins on SDS‐PAGE gels were found during DHA reduction in the absence of glutathione. AsA was oxidized by AsA oxidase to generate monodehydroascorbate (MDA) free radicals. MDA was also reduced by dioscorins to AsA in the presence of NADH mimicking the MDA reductase catalyzed reaction. These data suggest that dioscorins have both DHA reductase and MDA reductase activities.

Molecular cloning of two metallothionein-like protein genes with differential expression patterns from sweet potato (Ipomoea batatas) leaves

Metallothionein (MT) is a group of proteins with low molecular masses and high cysteine contents, and is classified into different types, which in general contains two domains (domain 1 and domain 2) with typical amino acid sequences (Rauser 1999). In this report two full-length cDNAs (Y459 and G14) encoding MT-like proteins were isolated from leaves of sweet potato (Ipomoea batatas). Their open reading frames contained 249 and 195 nucleotides (82 and 64 amino acids) for Y459 and G14, respectively, and exhibited a relatively low amino acid sequence similarity (ca. 25.8%). Gene structure studies showed that Y459 had the conserved domain 1 region of type 2 MT; however, the domain 2 region was not conserved and contained additional amino acids between the CxC and CxC spacing. G14 had conserved domains 1 and 2 of type 4 MT except that the last CxC of domain 2 was changed to RxC. Semi-quantitative RT-PCR showed that Y459 was expressed in significant quantity in roots and stems, but was much less in green leaves. During natural and induced (with dark and ethephon, an ethylene-releasing compound, treatments) leaf senescence, Y459 gene expression was significantly enhanced. In contrast, relatively constant gene expression levels were found for G14 in all tissues or treatments analyzed. In conclusion, the two MT-like protein genes of sweet potato display differential gene structures and gene expression patterns, which may be associated with the diverse roles and functions they play in plant physiology in order to cope with particular developmental and environmental cues.

Dioscorins from different Dioscorea species all exhibit both carbonic anhydrase and trypsin inhibitor activities.

Dioscorins, the storage proteins of yarn tubers, from six cultivars of three Dioscorea species including D. batatas, D. alata, and D. pseudojaponica were detected in crude extracts of yam tubers but not leaves by immuno stainings on PVDF membrane with a polyclonal antibody which was raised against 28 kDa dioscorin from Dioscorea batatas Decne. It was demonstrated that the dioscorins from the above-mentioned yam species exhibited both carbonic anhydrase (CA) and trypsin inhibitor activities by activity stainings on 15% SDS-PAGE gels. Dioscorins were identified as glycoproteins by ConA-peroxidase activity staining. Dioscorins from D. batatas Decne contained no zinc atoms detectable by atomic absorption spectrophotornetry. Neither 5mM acetazolamide nor 2,6-pyridinedicarboxylic acid inhibited the CA activity of dioscorins.

The mucilage of yam (Dioscorea batatas Decne) tuber exhibited angiotensin converting enzyme inhibitory activities

The tuber mucilage of yam (Dioscorea batatas Decne) (YTM) was extracted and purified to homogeneity, which was confirmed by the toluidine blue staining on a sodium dodecylsulfate-polyacrylamide gel electrophoresis gel treated with 2-mercaptoethanol appearing as a single band with molecular mass larger than 250 kDa. This purified YTM was shown by spectrophotometric method to inhibit angiotensin converting enzyme (ACE) in a dose-dependent manner (28.7 to 59.8% ACE inhibition, respectively, by 102.46 to 409.84 µg/mL YTM) using (N-(3-[2-furyl]acryloyl)-P he-Gly-Gly) (FAPGG) as a substrate. The concentration of YTM required for 50% inhibition (IC50) of ACE activity was 256.2 µg/mL while that of captopril was 0.00781 µM (0.0095 nmole). The commercial polysaccharide pectin (102.46 to 307.38 µg/mL) showed no inhibitory activity against ACE. Using fluorescent silica TLC or C18 reverse phase HPLC to detect FAPGG and FAP, the results also showed that YTM inhibited ACE. The YTM showed mixed type inhibition against ACE, and the Michaelis constant in the presence of YTM was 0.33 mM. Consumption of yam tubers may benefit peoples health. The YTM showed mixed type inhibition against ACE, and the Michaelis constant in the presence of YTM was 0.33 mM. Consumption of yam tubers may benefit peoples health.

Antioxidant activities of methanolic and hot-water extracts from leaves of three cultivars of Mai-Men-Dong (Liriope spicata L.)

1,1-dipheny-2-picrylhydrazyl (DPPH) scavenging activities of the 80% methanolic leaf extracts of three cultivars (small leaf, SL; big leaf, BL; thin leaf, TL) of Mai-Men-Dong (Liriope spicata L.) are analyzed by spectrophotometry. The concentrations required for 50% inhibition (IC50) of DPPH radicals were 81.08, 96.97, and 53.78μg/mL, respectively. The methanolic extracts were further partitioned into three n-hexane-, ethylacetate-, and water-soluble fractions, among which the ethylacetate-soluble fraction exhibited the highest DPPH scavenging activity. The IC50 of ethylacetate-soluble fractions of SL, BL, and TL for DPPH radical scavenging activity were 41.55, 24.55, and 53.33μg/mL, respectively. Each Mai-Men-Dong powder (1g) was deposited in a tea bag and then dipped in hot water (100℃, 100mL) for 3 min with triplicate samples. These hot-water extracts were then freeze-dried for an anti-DPPH radical capacity test, which found a positive correlation with the phenolic contents of each hot water extract. The IC50 of hot water extracts of SL, BL, and TL for DPPH radical scavenging activities were 378.97, 171.12, and 95.84mg/mL, respectively. All three hot water extracts can effectively scavenge hydroxyl radical using electron spin resonance (ESR) spectrometry. The IC50 against hydroxyl radical were 80.8, 69.7, and 116μg/mL, respectively, for the SL, BL, and TL cultivars.