Kinetic analysis of collagen fibrillogenesis: I. Use of turbidity--time data.

A method is presented for analyzing turbidity-time curves characterizing biological assembly and disassembly processes. The method allows for the determination of apparent rate constants for the turbidity lag and growth phases of collagen fibrillogenesis. Plots of concentration/lag time versus concentration for type I collagen and concentration/(time to complete growth phase) versus concentration are shown to be straight lines. The slopes of these plots are defined as the apparent rate constants for the lag and growth phases. Activation energies are obtained from the temperature dependence of these slopes. The slopes of the growth portion of turbidity-time curves as well as the final turbidity are directly proportional to the collagen concentration. These observations are consistent with the hypothesis that the rate limiting steps for both lag and growth phases are apparent first order with respect to collagen concentration. Sample calculations based on light scattering theory suggest that the turbidimetric growth phase begins when the number of collagen molecules per unit length is greater than 100 and that the extent of fibril formation is proportional to the turbidity per unit concentration. These studies indicate that the turbidimetric lag phase involves both linear and lateral growth of collagen linear aggregates.