The Relationship between Swelling of Hard Tissues Collagen in Acid and Alkali 173 



experiments carried out in acid solution showed no reduction in phosphorus content 

 over the period of swelling investigated whereas the alkaline series exhibited a 

 dramatic reduction in phosphorus as swelling progressed. 





^^200 



^250 



^200 



/2 le 

 rime Hours 



12 /6 20 



Time Hours 



Fig. I. Swelling curves of puritied bone coUagens: Fig. 2. Swelling curves ot purihed cerium collageiis: 



X, experiments carried out in 1.0 N NaOH; o, ex- x, experiments carried out in 1.0 N NaOH; o, ex- 



periments in HCI, pH 2.3; .1, coUagens swollen for periments in HCl, pH 2.3 



9 hours, in 1 .0 N NaOH, washed and replaced in 

 HCl, pH 1.1, 



The resistance of bone collagen to swelling in acid solution and the comparative 

 ease of swelling in alkali is consistent with the presence of inter-molecular cross- 

 linkages as proposed for dentine collagen. The relatively small content of phosphorus 

 present in bone collagen would not, 

 however provide sufficient phos- 

 phate ester linkages to confer on this 

 material the demonstrated stability 

 in acid solution. The phosphorus con- 

 tent noted here is equivalent to only 

 0.006 per cent of phosphate residues 

 (HPOg) by weight. In contrast, den- 

 tine collagen has been shown to con- 

 tain 0.4% HPOj on a similar basis. 

 This contention is supported by the 

 series of experiments whereby the 

 phosphorus content of bone collagen 

 was reduced by alkali pretreatment 

 and subsequent acid treatment pro- 

 vided no increase in swelling. The 



presence of a few phosphate-mediated cross-links in bone collagen is suggested by the 

 release of phosphorus during swelling in alkaline solution. The acid stability must, 

 however, be attributed to the presence of alternative cross-links which exhibit similar 

 lability in alkali. Schlueter and Veis (1964) have discussed the types of cross-links 

 common to dentine and corium coUagens and suggest that dentine contains in 

 addition to phosphate cross-links "extra" cross linkage sites which are not present in 

 corium coUagens. This view is consistent with our findings on bone collagen and 



r 



20 



rime 



Fig. 3. Phosphorus release dur 



ng swelling of purihed bone 

 md alkali, 1.0 N NaOH (o) 



