Biomedical Engineering Reference
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regulation is kinetically and energetically more efficient through the catabolic, rather
than the anabolic, pathway. The catabolic pathway involves HAases, enzymes that
catalyze HA cleavage. On the basis of biochemical data, Meyer classified HAases into
three differents categories: (i) testicular-type HAases (EC 3.2.1.35), which hydrolyze
the b(1,4) glycosidic linkages (Figure 2), (ii) leech-type HAases (EC 3.2.1.36), which
hydrolyze the b(1,3) glycosidic bonds, and (iii) bacterial-type HAases (EC 4.2.99.1),
that cleave the b(1,4) glycosidic linkages by a b elimination reaction (Deschrevel,
in press; Meyer, 1971). In the human, as in all mammals, all the HAases found until
now are of the testicular-type. The human genome includes six HAase genes: Hyal1 ,
Hyal2 , Hyal3 , Hyal4 , PH-20/Spam1, and HyalP1 (Girish and Kemparaju, 2007; Stern
et al., 2007). Among the products of these genes, Hyal1, Hyal2 and PH-20, or SPAM1
(Sperm Adhesion Molecule 1), show HAase activity and are the best characterized.
Hyal3 is widely expressed, but no enzymatic activity has yet been detected for this
protein using the available HAase assays. Hyal4 seems to be a chondroitinase with no
activity towards HA. HyalP1 is a pseudogene, transcribed but not translated in the hu-
man (Deschrevel, in press; Girish and Kemparaju, 2007; Stern et al., 2007). However,
although the knowledge about HAases did not ceassed to increase over the years, the
way by which HAases are involved in the control of the HA molar mass distribution
is still to be elucidated. Indeed, rather little is known about the species, the parameters
and the phenomena that control HAase activity. Mio and Stern (2002) suggest that
HAase could be present in tissues together with inhibitors which may allow HAase
to be rapidly activated or inactivated. However, even though some HAase inhibition
activities have been detected in vivo , very little is known about their molecular basis
and mechanism of action (Mio and Stern, 2002).
Figure 2. Hydrolysis of the b (1,4) glycosidic bonds of HA as catalyzed by testicular-type HAases (EC
3.2.1.35) (Deschrevel, in press).
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