A sensitive pH indicator-based spectrophotometric assay for PHB depolymerase activity on microtiter plates

A continuous spectrophotometric assay for the screening of PHB depolymerase activity in microtiter plates was developed. We evaluated crystalline PHB in the suspension and coated it with the addition of a pH indicator to detect the breakage of the ester bond by proton titration. The reaction rate and the concentration of the recombinant PhaZ1 from Paucimonas lemoignei PHB depolymerase presented a linear correlation. A comparison of the proposed method with the turbidimetric method adapted to the microtiter plates revealed that the use of indicators increases the response signal by at least 5-fold, resulting in increased sensitivity and better signal-to-noise ratio. Furthermore, the proposed method offers a wide range of pH from 5.0 to 9.2 by using different buffer-indicator pairs and was employed for the screening of PHB-depolymerase activity on 140 bacterial strains isolated from Lake Chapala. Eleven strains were positive for PHB-depolymerase activity, which were ACSLRF-27, ACPLRF-6, and ACPLRF-5 (16S rRNA sequence alignment revealed 99-100% similarity with Actinomadura geliboluensis strain A8036, Streptomyces cavourensis strain NRRL 2740, and Streptomyces coelicolor strain DSM 40233, respectively); these that showed the highest activities. In conclusion, the method was successfully applied for finding new strains and for quantifying the PHB depolymerases activity with crystalline PHB.

Thymidylate synthase polymorphism in Mexican patients with colon cancer treated with 5-fluorouracil

PURPOSE

We analyzed the genotype and allele frequency of variable number tandem repeats (VNTR)-thymidylate synthase (TS) and its relationship with the disease evolution in colon cancer patients.

METHODS

We selected 24 paraffin-embedded colon cancer tissue samples from Mexican patients who received a 5-fluorouracil (5-FU)-based chemotherapy regimen. Tumor tissue was digested with proteinase K and genomic DNA was isolated by the standard method with phenol-chloroform extraction. Polymerase chain reaction (PCR) was performed for TS genotyping of VNTR and the results were evaluated directly in a stained agarose gel.

RESULTS

The allele frequency of 2 repeats (2R) was greater (0.66) than 3R (0.34) in metastatic colon cancer (x²=10.24; p=0.001)) however, no difference in allelic distribution between 2R (0.54) and 3R (0.46) in non metastatic patients was observed (x²=0.640; p=0.424).

CONCLUSION

Our results suggest that Mexican patients with colon cancer present differences in the allelic distribution, the 2R allele being the most frequent.