Physico-chemical characteristics of immobilized polygalacturonase from Aspergillus niger (SA6)

Polygalacturonase (PG) was isolated from Aspergillus niger (A. niger) (SA6), partially purified, characterized and immobilized by entrapment using calcium alginate. The polygalacturonase showed two bands on sodium dodecyl sulfate polyacryamide gel electrophoresis (SDS-PAGE) suggesting an “endo and exo” polygalacturonase with apparent molecular weights of 35 and 40 KDa, respectively. The enzyme was purified 9 fold with a yield of 0.18% and specific activity of 246 μmole/min/mg. The apparent KM and Vmax of the immobilized polygalacturonase were11.1 mg/ml and 1.65 μmole/min/mg, respectively. The optimum pH and optimum temperature of the immobilized polygalacturonase were 4.5 and 40°C, respectively. Immobilized polygalacturonase exhibited more stability to changes in pH than the temperature. The activity of the immobilized polygalacturonase reduced to 34.56 and 14.81% of the initial activity in the second and third catalytic cycles, respectively. The half life of the enzyme and theactivity lost per minute on thermal storage were 10 min and 0.0213 μMole of D-galacturonic acid.Keywords: Polygalacturonase, Aspergillus niger, pectinases, enzyme

Regulation of immune responses by L- arginine metabolism

L-Arginine is an essential amino acid for birds and young mammals, and it is a conditionally essential amino acid for adult mammals, as it is important in situations in which requirements exceed production, such as pregnancy. Recent findings indicate that increased metabolism of L-arginine by myeloid cells can result in the impairment of lymphocyte responses to antigen during immune responses and tumour growth. Two enzymes that compete for L-arginine as a substrate - arginase and nitric-oxide synthase - are crucial components of this lymphocyte-suppression pathway, and the metabolic products of these enzymes are important moderators of T-cell function. This Review article focuses on the relevance of L-arginine metabolism by myeloid cells for immunity under physiological and pathological conditions