Comparative studies on the ability of pancreatic colipases to restore activity of lipases from different species

Comparison of amylase and lipase activities in serum and plasma of dogs

BACKGROUND

Amylase and lipase activities are most often determined in serum, although heparinized plasma is more convenient to obtain and is used for many routine biochemical analyses.

OBJECTIVE

The purpose of this study was to compare amylase and lipase activities in serum and plasma of dogs and to determine whether either specimen type is acceptable for analysis.

METHODS

Serum and heparinized plasma were obtained from 101 randomly selected dogs and analyzed in parallel for alpha-amylase and lipase. Results were compared using Passing-Bablock regression, Bland-Altman difference plots, and correlation analysis.

RESULTS

There was a high correlation between the results obtained from serum and those from plasma. Regressions (with 95% confidence intervals in parentheses) were as follows: lipase(plasma) = 0.984 (0.976/0.995) Chi lipase(serum) - 0.9 (2.9/0.7) (r =.999); a-amylase(plasma) = 1.003 (0.977/1.032) Chi alpha-amylase(serum) - 1.9 ( 20.7/23.3) (r =.991). Mean differences (serum - plasma) were 8 U/L and 4 U/L for lipase and alpha-amylase, respectively. Classification of results as normal or abnormal did not differ according to specimen type.

CONCLUSION

In dogs, lipase and alpha-amylase activities can be determined with the same level of accuracy in serum and in heparinized plasma.

Large spectral changes accompany the conformational transition of human pancreatic lipase induced by acylation with the inhibitor tetrahydrolipstatin

Human pancreatic lipase (HPL) loses more than 80% of its activity when incubated with tetrahydrolipstatin in a buffer containing bile salts. During the inactivation process, large changes are observed in intrinsic tryptophan fluorescence and in the near-ultraviolet circular dichroism. The rate of chemical inactivation is highly comparable to that determined from the time dependence of the spectral changes. It is concluded that HPL undergoes a conformational transition upon inhibitor binding, resulting in a change in the microenvironment of tryptophan residues. Bile salts are needed in this system for effective inactivation of the enzyme by tetrahydrolipstatin, and a large increase in the inactivation rate takes place at about the critical micellar concentration (CMC) of bile salts. The inhibited enzyme can be reactivated by reducing the bile salt concentration to below the CMC, and the changes in tryptophan fluorescence induced by acylation with tetrahydrolipstatin are thereby reversed. This suggests that bile salts above their CMC stabilize the acyl-enzyme complex.

Studies on the immunological cross-reactivity of various pancreatic colipases. Isolation by immunoaffinity chromatography of a single form of procolipase from porcine pancreas

Antibodies against porcine procolipase B were produced in rabbits. The antiserum was used to immunoinactivate various forms of native and trypsin-treated porcine colipase. Our results indicate that all forms of the porcine cofactor bind to anti-porcine procolipase B antibodies. Human colipase showed lower affinity for the antibodies than porcine colipase. No cross-reactivity was observed between pig and horse, cow, dog or chicken colipases. Immunological studies on porcine colipase, carried out in the presence of lipid, provided evidence that antibodies bind to colipase at or near the lipase binding site. The binding of antibodies to colipase is not affected by the adsorption of the cofactor at a lipid interface. Using a predictive method for identification of the antigenic determinants, it was found that, in pig colipase, regions at positions 42-48 and 70-74 might represent antigenic sites. In the horse protein, the peptide segment 42-48 was also recognized as a possible antigenic site. An immunoadsorbent gel column was prepared for a one-step isolation of porcine colipase. In contrast to purification methods described so far, immunoaffinity chromatography yielded only one form of the porcine cofactor when starting from a pancreatic extract. This protein preparation has structural, biochemical and immunochemical properties similar to that of porcine procolipase A previously isolated from pancreas in the presence of detergent.