Characterization of the proteolytic activity firmly attached to yeast phoshoenolpyruvate carboxykinase

The proteinase yscB inhibitor (PB12) gene of yeast and studies on the function of its protein product

The gene for proteinase yscB inhibitor I2B (PBI2) from Saccharomyces cerevisiae was isolated by oligonucleotide screening of a genomic DNA library, and was sequenced. The gene codes for a single protein of 75 amino acids. In contrast to the published amino acid sequence [Maier, K., Müller, H., Tesch, R., Trolp, T., Witt, I. & Holzer, H. (1979) J. Biol. Chem. 254, 12,555-12,561] the DNA sequence revealed a valine instead of a leucine at position 33 (32 of the mature protein). Therefore the primary sequences of the isoinhibitors I2B of S. cerevisiae and I1B of Saccharomyces carlsbergensis differ only at position 34 (glutamic acid/lysine). The open reading frame of PBI2 was replaced in vitro by the URA3 gene and a I2B null mutant of S. cerevisiae was constructed by gene replacement. The mutation resulted in an elevation of the protein degradation rate by 50% when grown under nutritional stress compared to the isogenic wild type. Growth and viability of the cells was not significantly affected by the absence of I2B.

Purification of phosphoenolpyruvate carboxykinase from Saccharomyces cerevisiae and its use for bicarbonate assay

Electrophoretically homogeneous phosphoenolpyruvate carboxykinase (EC 4.1.1.49) from Saccharomyces cerevisiae was obtained in high yields by means of a two-step purification procedure consisting of ion-exchange chromatography and affinity chromatography on adenosine 5'-monophosphate-Sepharose 4B. In the latter step the binding of the enzyme to the resin specifically required the presence of Mn2+. The enzyme was eluted when Mn2+ was removed by addition of ethylenediaminetetraacetate to the elution buffer. Homogeneity, molecular weight, and subunit composition of phosphoenolpyruvate carboxykinase were checked by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and gel filtration. A factor which caused an underestimation of the enzyme activity in crude extracts was identified as adenylate kinase. Finally, a method is proposed for the enzymatic assay of bicarbonate using a purified phosphoenolpyruvate carboxykinase preparation.

Multiple forms of protyrosinase from Aspergillus oryzae and their mode of activation at pH 3.0

This paper describes the isolation of three molecular forms (I-III) of protyrosinase and catalytically active tyrosinase ( monophenol ,dihydroxyphenylalanine: oxygen oxidoreductase, E.C. 1.14.18.1) from fresh mycelia of Aspergillus oryzae BIR 128 by (NH4)2SO4 fractionation, successive chromatographies and disc-gel electrophoresis. Experimental evidence is presented that purified protyrosinase is contaminated with firmly attached proteinases, and that this contamination may account for both the multiple molecular forms of protyrosinase /tyrosinase and the activation of the proenzyme at acidic pH (2.5-3.0). The activation process of protyrosinase seems to be the result of a cleavage of the polypeptide chain by aspartic proteinase from Aspergillus (EC 3.4.23.6) in the purified protyrosinase preparation. Protyrosinase and tyrosinase have different conformation, different stabilities and some different properties.