PROTEOGLYCANS FROM THE VERTEBRAL CARTILAGE OF THE CLEARNOSE SKATE, RAJA-EGLANTERIA - INHIBITION OF HYDROXYAPATITE FORMATION

Studies were undertaken to examine the importance of organic proteogly can matrices in the calcification of elasmobranch vertebral cartilage. Proteoglycans were extracted from the vertebral cartilage of the clea rnose skate, Raja eglanteria Bose, with a 3M guanidine hydrochloride/1 0% EDTA solution. Proteoglycan solutions (12 mu g ml(-1)) were effecti ve inhibitors of hydroxyapatite formation in vitro from high concentra tion calcium phosphate solutions. Inhibition of crystal formation appe ars to occur through the restriction of phase transformation from a ca lcium phosphate precursor to hydroxyapatite crystals. The concentratio n and/or degradation of proteoglycans in elasmobranch vertebral cartil age may have a physiological role in the production of alternating min eral-rich and mineral-poor growth zones, currently used in ageing stud ies.