To increase the rate and amount of biogas produced from sludge at waste water treatment plants, the hydrolysis, which is considered to be the rate limiting step in the anaerobic digestion chain, needs to be increased. The addition of the well studied enzyme subtilisin Carlsberg gives increased biogas production rate and yield but the enzymes activity life time in the environment is too short due to proteolysis from endogenous proteases produced by microorganisms in the anaerobic digester. Genes in plasmid vectors for engineered variants of the enzyme, with strategic substitutions of amino acids were ordered and provided. The mutations were chosen to decrease the amount of possible cleavage sites by serine proteases on the enzyme and thereby decrease proteolysis from endogenous serine proteases and from intermolecular autoproteolysis. The vectors were successfully transformed into the host cells and the enzymes were expressed and purified by immobilized metal ion affinity chromatography. The enzymes were then analyzed by SDS-PAGE and western blot. The enzymes were quantified and their proteolytic activity was analyzed. Due to unexpected production problems the enzymes were not characterized. The current thesis provides a basis for further investigation of the problems with the inactive enzymes so that they eventually can be characterized.