Donn Nelton Rubingh

Protein engineering from a bioindustrial point of view

Work with proteins, particularly enzymes, is a rapidly growing segment of the biotechnology industry. Directed evolution promises to become an increasingly important strategy in their development as it allows one to sidestep some of the difficult questions relating the structural and functional properties of such proteins to their industrial utility. It is also clear, however, that greater understanding of how to engineer certain basic enzyme properties, such as stability, activity, and surface properties, is beginning to emerge, and this understanding will make rational design more efficient. To engineer a commercially useful protein many properties need to be changed, and frequently these changes are interdependent. Recent protein engineering studies on protease, amylase, lipase and cellulase illustrate some of the progress in this area.

The influence of surfactants on enzyme activity

Most of the recent literature on the effect of surfactants on enzyme activity focuses on enzymes that function at interfaces. Model studies on substrates in solution and at solid/liquid interfaces are beginning to reveal the relationship between such fundamental parameters as surface concentration, surface mobility and enzyme kinetics. For enzymes that function at liquid/liquid interfaces, such as lipases and phospholipases, the recent increase in the number of X-ray structures combined with site-directed mutagenesis studies has resulted in a clearer picture of the molecular events responsible for catalysis. The influence of surfactants on the enzyme structure and the environment in which the enzyme must function is still not as well defined as one would wish, although significant progress has been made. The activity of integral membrane proteins can be strongly influenced by the surfactant systems used in their isolation. The way in which surfactants inhibit or augment such activity is beginning to emerge in a number of individual cases.

PHASE BEHAVIOR OF THE C 10 E 4 -WATER AND C 10 E 4 -HEXADECANE-WATER SYSTEMS

The phase behavior of pure tetraoxyethylene glycol monodecyl ether (C 10 E 4 ) with water and water plus hexadecane has been determined between 0 and 90°C. The C 10 E 4 -H 2 O system displays what has been termed a double cloud point within certain concentration limits. The phase diagram shows that this phenomenon is a consequence of discontinuities in the tie line length which results in sudden changes in volume and refractive index of the disperse phase droplets. Vie show that a consistent interpretation of our data requires the existence of four 3 phase lines with zero variance.