Sedimentation equilibrium analysis demonstrated that preparations of bovine lipoprotein lipase contain a complex mixture of dimers and higher oligomers of enzyme protein. Enzyme activity profiles from sedimentation equilibrium as well as from gel filtration indicated that activity is associated almost exclusively with the dimer fraction. To explore if the enzyme could be dissociated into active monomers, 0.75 M guanidinium chloride was used. Sedimentation velocity measurements demonstrated that this treatment led to dissociation of the lipase protein into monomers. Concomitant with dissociation, there was an irreversible loss of catalytic activity and a moderate change in secondary structure as detected by circular dichroism. The rate of inactivation increased with decreasing concentrations of active lipase, but addition of inactive lipase protein did not slow down the inactivation. This indicates that reversible interactions between active species precede the irreversible loss of activity. The implication is that dissociation initially leads to a monomer form which is in reversible equilibrium with the active dimer, but which decays rapidly into an inactive form, and is therefore not detected as a stable component in the system.

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The aim of this investigation was to study crypt fission, a process which may be instrumental in regulating crypt number in the intestine. Young Holtzman rats were killed at various times after parturition and samples of the small intestine and colon were removed and processed. A microdissection technique was used to separate crypts from other structures. Crypts were scored as normal or fissioning. the percentage of crypts in fission (PCF) reached peak values of 25% and 52% in the small bowel and colon, respectively, at 21 days post‐parturition. From this time onward, the PCF dropped until the adult value of approximately 7% was reached in each site. During this same period, the number of crypts increased from 1.9 × 106 to 3.3 × 106 in the small bowel and 2.2 × 105 to 6.5 × 105 in the colon. Thus an inverse relationship between the percentage of crypts in fission and crypt number was found. Distribution of fissure heights in fissioning crypts did not change as the animal aged. the majority of the fissures were found in the lower 1/4 of the fissioning crypts. This suggests that as soon as the fissure extends beyond the stem cell zone, division into two crypts soon occurs.

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