Effect of shear on membrane-associated enzymes: Studies of isolated progesterone 11?-hydroxylase complex fromRhizopus nigricans

Role of hydrodynamic shear on activity and structure of proteins

Proteins are important products used in industry. They may be enzymes which catalyze different reactions or they may be required for their biological activities as hormones, growth factors or therapeutics. During production and recovery, proteins are subjected to fluid forces which arise due to operations such as stirring, pumping and centrifugation. The resulting hydrodynamic shear forces may cause damage to the large molecular weight proteins, resulting in denaturation and inactivation of the protein. This is a major concern as it affects the overall efficiency of protein recovery and final yield of the product. A considerable amount of research has been devoted to studying the effects of hydrodynamic shear stress on proteins, especially with respect to the enzymes. Enzymes are subjected to shear stresses during their production in fermentors, during isolation and purification steps in downstream operations and also during their use in enzyme reactors, especially if stirred reactors are employed to perform enzyme catalysed reactions. The present review discusses the effects of fluid shear stress on proteins including enzymes. A brief description on deactivation has been included in order to understand the effect of shear on the deactivation kinetics of proteins. The model systems used to subject proteins to shear and some unit operations during protein processing or use wherein they are exposed to shear stresses have also been presented. The significance of shear effects in designing bioprocesses involving shear sensitive biocatalysts as well as suggestions for future work have also been given.

Evidence for and characterization of cytochrome P-450 in Neurospora crassa

Cytochrome P-450 was detected in microsomes and presumably in cytosol of Neurospora crassa, and was found to be inducible by progesterone. In the microsomal fraction cytochrome b5 and NADPH-cytochrome c reductase activities were measurable, too. Cytochrome P-450 of Neurospora crassa is inhibited by SKF-525 A and by inhibitors of ergosterol biosynthesis. After induction of cytochrome P-450 with progesterone 11 alpha-hydroxyprogesterone as one metabolite of progesterone was detected in the culture media as well as in the mycelia. After 42 hours about 70% of progesterone were metabolized.

The effects of shear rate on the enzymatic activity of the tissue factor-factor VIIa complex

A novel enzyme reactor for studying phospholipid-dependent reactions was used to explore the effects of flow on tissue factor (TF)-initiated coagulation. Capillary tubes (0.27 mm i.d.) were coated with a phospholipid bilayer containing TF, a transmembrane protein that is an essential cofactor for factor VII. Production of factor Xa exiting the tube was monitored with time during perfusion of the capillary with factor X (50 to 1500 nM) in the presence of factor VIIa (10 nM). Steady-state production of factor Xa as a function of [FX] was determined by chromogenic assay (Spectrozyme Xa) for a range of wall shear rates (25 to 3000 sec-1). Diffusion was found to play a major limiting role in FXa production for TF:30% phosphatidylserine (PS)/70% phosphatidylcholine (PC) surfaces. In contrast, TF/PC surfaces slowed the reaction sufficiently to enter a kinetically controlled regime where shear fluid had little effect on Km. In contrast with classical enzyme kinetic theory there was a three-fold increase in Vmax as shear increased from 25 to 300 sec-1. This finding implies a direct effect of shear on the kinetics of factor X activation by TF/FVIIa. The perfusion system is simple to use and offers the potential for studying the role of flow on a wide variety of enzymatic reactions related to coagulation.

Correlation of biocatalytic activity in an organic-aqueous two-liquid phase system with solvent concentration in the cell membrane

Results presented here show that loss of progesterone 11 alpha-hydroxylase activity in Rhizopus nigricans in aqueous-organic two-liquid phase and cosolvent systems correlates well with the concentration of solvent in the cell membranes. Rhizopus nigricans is shown to retain full 11 alpha-hydroxylase activity at saturating aqueous phase concentrations of hexane and the higher primary alcohols. This reflects their inability to attain a critical concentration in the cell membranes. The relationship between our own findings and the previously described correlation of the logarithm of the partition coefficient with activity retention is explained and design parameters are proposed that may be used to select solvents for future biocatalytic systems.