Structural and functional factors in the lyotropic activity of amides and alkyl-substituted amides on acid-soluble collagen

Effect of alcohols and neutral salt on the thermal stability of soluble and precipitated acid-soluble collagen

The effects of mono- and poly-hydric alcohols in the presence of KCl on the intrinsic stability of collagen molecules in dilute acid solution were compared with corresponding solvent and salt effects on the increased stability of the aggregated molecules in salt-precipitated fibrils. Salt addition decreased solubility and increased the thermal stability of fibrils, but progressively decreased the stability of collagen molecules in solution. In contrast, the alcohols enhanced solubility and decreased fibril stability, the effects increasing with solvent hydrocarbon chain length and with decreasing hydroxyl/methylene-group ratio. Molar destabilization of dissolved collagen by alcohols was lower than for fibrils, and at low salt concentration, both ethylene glycol and glycerol were structural stabilizers. Electron-micrograph studies indicated that salt-precipitated fibrils tended to adopt the native aggregation mode, and qualitatively similar solvent effects were observed in insoluble collagens. Implications of the experimental findings are discussed in terms of a model in which electrostatic and apolar interactions mainly govern the excess of stability in collagen fibrils whereas intrinsic stability of single molecules is a function of polar interactions and polypeptide-chain rigidity.

Effect of compounds of the urea-guanidinium class on renaturation and thermal stability of acid-soluble collagen

The effects of guanidinium salts in decreasing the renaturation rate and lowering the thermal stability of acid-soluble calf-skin collagen have been compared with those of formamide and urea. With the exception of guanidinium sulphate at higher concentrations, no qualitative differences were apparent in the effects of these perturbants, which thus differed only in molar activity. Activity variation in the guanidinium salts reflected a net effect resulting from additivity of cation and anion contributions. As observed in other protein systems, lyotropic activity increased in the series formamide<urea<guanidinium ion, and in the guanidinium salts in the anion order fluoride<sulphate<chloride<bromide<nitrate<iodide. Low activities of guanidinium fluoride and sulphate were attributable to counter-effects of the anions, which acted as structural stabilizers. Changes in renaturation kinetics induced by either temperature or added perturbants appeared to conform with the Flory-Weaver model for the collagen transition. Additivity and non-specificity of the observed effects are discussed with particular reference to a common mechanism involving weak, non-saturated binding of perturbants at protein peptide groups.

The effects of glycols on the renaturation of soluble collagen

The effects of a number of related glycols and substituted glycols on the renaturation kinetics of acid-soluble calf-skin collagen have been investigated. Optical rotation recovery was monitored at a fixed temperature in the presence of perturbants and the initial rates of reaction were determined. The effects of perturbants on stability of the native protein are compared with their action in the renaturing systems. The relationship between initial recovery rates and fixed-time [alpha]-values is shown to be dependent upon the renaturation temperature. The influence of perturbant concentration on recovery rates is discussed in terms of present theories of the mechanism of collagen renaturation.

The effects of certain glycols, substituted glycols and related organic solvents on the thermal stability of soluble collagen

The effects of a number of related diols, substituted diols and glycerol on the thermal stability of acid-soluble calf skin collagen were investigated. Thermal transition temperatures were determined by optical rotation measurement. Short-chain diols with terminal hydroxyl groups, i.e. ethylene glycol and propane-1,3-diol, stabilized the protein at all accessible concentrations. Stabilization was also observed with glycerol and diethylene glycol. Higher homologues in the diol series produced various effects, as did hydroxyl-group positional isomerism. Monoalkyl substitution of diols progressively lowered the denaturation temperature of collagen. Results are discussed in relation to possible mechanisms of perturbant action.