大熊猫臼齿釉质的超微结构和氨基酸组成

大熊猫臼齿釉质的超微结构特征主要是施氏明暗带的宽度一般由8—15条釉柱组成;釉柱的横切面一般呈六角形或四角形,由里向外,釉柱的直径逐渐增大。在靠近釉牙本质界处,釉柱数量逐渐减少,有时甚至完全缺失,形成无釉柱结构的釉质。大熊猫臼齿釉质的氨基酸组成主要以甘氨酸,丙氨酸,谷氨酸,天冬氨酸和亮氨酸的含量为最高,而蛋氨酸,胱氨酸和酪氨酸的含量为最低。另外,还含有少量的羟脯氨酸。这种组成模式一般与人类和其它哺乳动物牙齿釉质的氨基酸组成相类似。

ULTRASTRUCTURE AND AMINO-ACID COMPOSITION OF THE ENAMEL OF AILUROPODA MOLAR

The ultrastructure and the amino-acid composition of the enamel of the molarteeth have been studied in fossil and/or living Ailuropoda.The methods used includedscanning electron microscopy and automatic amino-acid analyser.The results obtainedare as follows:1.The Hunter-Schreger bands have a thickness in Ailurapoda molars of about8—15 prisms.In cross-cut views,although the enamel prisms show some irregularityin shape,they reveal,in general,a“hexagonal-”or“quadrangular-shaped”.It mayrepresent a basic pattern of the enamel structure of Ailuropoda.Besides,in the zoneclosest to the enamel-dentin junction,prisms have decreased in number;and prismsare occasionally entirely missing,resulting in rodless or prismless enamel.2.The amino-acid compositions of the enamel matrix of the Pleistocene Ailuro-poda molar are characterized by a remarkable high content of glycine,alanine,glutamicacid,aspartic acid and leucine.However,it is of interest to note that there is a smallproportion of hydroxyproline in enamel.Since hydroxyproline has been detected inenamel very carefully prepared in the present analysis so that contamination withdentine was almost certainly avoided,it seems reasonably certain that the enamel ma-trix contains a small proportion of this amino-acid.