Sufficient highly purified native pea cytosolic ascorbate peroxidase was obtained to characterize some of its kinetic and spectral properties. Its rate constant for compound I formation from reaction with Hz02 is 4.0X 10' M-' s-l, somewhat faster than is typical for peroxidases. Compound I has the typical optical spectrum of an iron(porphyrin-n-cation radical, despite considerable homology with yeast cytochrome c peroxidase. The rate constant for cornround I reduction by ascorbate is extremely fast (8.0 X 10' M-s ' at pH 7.8), again in marked contrast to the behavior of the yeast enzyme. The pHrate profde for compound I formation indicates a pK, value of 5.0 for a group affecting the active site reaction.

Bone morphogenic protein-7 (BMP-7) supports ectopic cartilage and bone formation, is expressed in normal articular cartilage, and increases matrix synthesis in chondrocytes. Based on this knowledge, we hypothesized that an adenovirus (Ad) vector encoding human BMP-7 could be used to modify chondrocytes genetically to improve their capacity for cartilage repair. An adenovirus vector encoding BMP-7 (AdBMP-7) was constructed and its bioactivity confirmed by ectopic bone formation assay. AdBMP-7 modification of bovine chondrocytes induced expression of BMP-7 mRNA and bioactive protein, resulting in an increase in incorporation of 35SO; into proteoglycan, 3H-proline uptake into protein, and the expression of the cartilage-specific matrix genes, aggrecan and type I1 collagen. An in vitro model of chondrocyte transplantation was used to demonstrate the feasibility of using genetically modified chondrocytes to enhance formation of cartilage-like tissue. When transplanted onto cartilage explants and maintained in vitro for 3 weeks, chondrocytes modified with AdBMP-7 formed 1.9-fold thicker tissue than chondrocytes modified with a control vector (P < 0.001). This tissue was positive for type I1 collagen and proteoglycan but negative for type X collagen and demonstrated a cartilage-like morphology. These observations suggest that Ad-mediated transfer of BMP-7 gene to chondrocytes enhances the chondrocyte-specific matrix synthesis and their capacity to form cartilage-like tissue, thus representing a strategy that may improve cell-based cartilage repair.

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