Biosynthesis of vitamin B₁₂ (VB₁₂) requires the methylation at positions C-2 and C-7 of the precursor uroporphyrinogen Ⅲ (urogen Ⅲ) to precorrin-2 by S-adenosyl-L-methionine uroporphyrinogen Ⅲ methyltransferase (SUMT), which is a potential bottleneck step. Most of SUMTs are inhibited by urogen Ⅲ and by-product S-adenosyl-L-homocysteine (SAH). In order to mine an SUMT that lacks such an inhibitory property to drive greater flux through the VB₁₂ biosynthetic pathway, we cloned two SUMT genes (RCcobA1, RCcobA2) from Rhodobacter capsulatus SB1003 and expressed them in Escherichia coli BL21 (DE3). Thereafter, the two enzymes were purified and their specific activity of 27.3 U/mg, 68.9 U/mg were determined respectively. The latter was 2.4 times higher than PDcobA (27.9 U/mg) from Pseudomonas denitrifican. Additionally, RCcobA2 could tolerate over 70 μmol/L urogen Ⅲ, which has never been reported before. Hence, RCcobA2 can be used as an efficient enzyme to regulate the VB₁₂ metabolic pathway and enhance VB₁₂ production in industrial strains.

ObjectiveTo investigate the characteristics of intrahepatic and extrahepatic organ failure at the onset of acute－on－chronic liver failure（ACLF）， to explore the features of a new clinical classification system of ACLF， and to provide a basis for the diagnosis， treatment， prognostic analysis of the disease. MethodsA retrospective analysis was performed for the clinical data of the patients who were hospitalized Beijing YouAn Hospital， Capital Medical University， from January 2015 to October 2022 and were diagnosed with ACLF for the first time. According to the conditions of intrahepatic and extrahepatic organ failure at disease onset， they were classified into type Ⅰ ACLF and type Ⅱ ACLF. Type Ⅰ ACLF referred to liver failure on the basis of chronic liver diseases， and type Ⅱ ACLF referred to acute decompensation of chronic liver diseases combined with multiple organ failure. The clinical features of patients with type Ⅰ or type Ⅱ ACLF were analyzed， and the receiver operating characteristic （ROC） curve was used to assess the value of MELD， MELD－Na， and CLIF－C ACLF scoring system in predicting the 90－day prognosis of ACLF patients with type Ⅰ or type Ⅱ ACLF. The independent－samples t test was used for comparison of normally distributed continuous data between two groups， and the Wilcoxon rank－sum test was used for comparison of non－normally distributed continuous data between two groups； the chi－square test or the Fisher’s exact test was used for comparison of categorical data between two groups. ResultsA total of 582 patients with ACLF were enrolled， among whom there were 535 patients with type Ⅰ ACLF and 47 patients with type Ⅱ ACLF. Hepatitis B and alcoholic liver disease were the main causes in both groups， with no significant difference between the two groups （P>0.05）. Chronic non－cirrhotic liver disease （28.2%） and compensated liver cirrhosis （56.8%） were the main underlying liver diseases in type Ⅰ ACLF， while compensated liver cirrhosis （34.0%） and decompensated liver cirrhosis （61.7%） were the main underlying liver diseases in type Ⅱ ACLF， and there was no significant difference in underlying liver diseases between the patients with type Ⅰ ACLF and those with type Ⅱ ACLF （P<0.001）. The patients with type Ⅱ ACLF had significantly higher median MELD score， MELD－Na score， and CLIF－C ACLF score than those with type Ⅰ ACLF （all P<0.001）. The patients with type Ⅱ ACLF had significantly higher 28－ and 90－day mortality rates than those with type Ⅰ ACLF （38.3%/53.2% vs 15.5%/27.5%， P<0.001）. For the patients with type Ⅰ ACLF who did not progress to multiple organ failure， the patients with an increase in MELD score accounted for 63.7% in the death group and 10.1% in the survival group （P<0.001）， while for the patients with type Ⅰ ACLF who progressed to multiple organ failure， there was no significant difference in the change in MELD score between the survival group and the death group （P>0.05）. In the patients with type Ⅰ ACLF， MELD score， MELD－Na score， and CLIF－C ACLF score had an area under the ROC curve （AUC） of 0.735， 0.737， and 0.740， respectively， with no significant difference between any two scores （all P>0.05）. In the patients with type Ⅱ ACLF， CLIF－C ACLF score had a significantly higher AUC than MELD score （0.880 vs 0.560， P<0.01） and MELD－Na score （0.880 vs 0.513， P<0.01）. ConclusionThere are differences in underlying liver diseases， clinical features， and prognosis between type Ⅰ and type Ⅱ ACLF， and different prognosis scoring systems have different emphases， which provide a basis for the new clinical classification system of ACLF from the perspective of evidence－based medicine.