Aldo-keto reductases (AKRs) mediated stereoselective reduction of prochiral carbonyl compounds is an efficient way of preparing single enantiomers of chiral alcohols due to their high chemo-, enantio-, and regio-selectivity. To date, the application of AKRs in the asymmetric synthesis of chiral alcohols has been limited, due to the challenges of cloning and purifying. In this work, the aldo-keto reductase (AKR3-2-9) from Bacillus sp. was obtained, purified and proved to be NADPH-dependent. It exhibits good bioactivity and stability at 37 °C, pH 6.0. AKR3-2-9 is catalytically active on 11 pairs of substrates such as 3-methylcyclohexanone and methyl pyruvate, among which it showed the highest catalytic activity for acetylacetone. In addition, AKR3-2-9 was able to be resistant to five common organic solvents such as methanol and ethanol, it retained high catalytic activity even in a reaction system containing 10% v/v organic solvent for 6 h, which indicates its broad substrate spectrum and exceptional organic solvent tolerance. Furthermore, its three-dimensional structure was constructed and catalytic-site-analysis of the enzyme was conducted. Notably, it was capable of catalyzing the reaction of the key intermediates of duloxetine. The extensive substrate spectrum and predominant organic solvents resistance makes AK3-2-9 a promising enzyme which can be potentially applied in medicine synthesis.

Backgrounds: Research has demonstrated that elevated serum total bilirubin (STB) levels have a beneficial impact on various diseases, particularly metabolic syndrome. This study aims to investigate the association between STB levels and serum testosterone (STT) in order to determine if bilirubin plays a protective role in relation to testosterone deficiency (TD) risk. Methods: In this study, a total of 6,526 eligible male participants aged 20 years or older were analyzed, all of whom took part in the National Health and Nutrition Examination Survey (NHANES) conducted between 2011 and 2016. To investigate the relationship between STB and STT levels, we employed weighted multivariate regression models along with restricted cubic splines (RCS). Additionally, a subgroup analysis was conducted to explore the heterogeneity of this relationship across different subpopulations. Results: Among the participants, 1,832 individuals (28.07%) were identified as having testosterone deficiency (TD), defined as an STT level below 300 ng/dL. A significant positive correlation between STB and STT levels was observed in both crude and adjusted models (all P < 0.0001). The association between STB and STT levels was found to be statistically significant up to a threshold of 17.1 µmol/L, after which it became statistically insignificant(P for non-linearity = 0.0035). Weighted logistic regression analysis indicated that a 1 µmol/L increase in STB was associated with a 4% decrease in the likelihood of TD (odds ratio = 0.96, P < 0.0001). Subgroup analysis showed that the inverse relationship was limited to individuals aged 60 and over, non-smokers/drinkers, and obese individuals. Conclusion: STB within the physiological range(17.1 µmol/L) was positively associated with STT in adult males. The potential protective role of bilirubin regarding testosterone levels merits further exploration.