Opinion ID: 209904
Heading Depth: 2
Heading Rank: 1

Heading: Axis-Shield’s HMTase Infringement Theory

Text: We first address the district court’s grant of summary judgment that was premised on Axis-Shield’s HMTase infringement theory. The crux of the district court’s 2007-1349 9 decision rested on the claim term “homocysteine conversion products.” In construing that term, the court concluded that “homocysteine conversion products” are “those products of the homocysteine conversion reaction that are derived from homocysteine.” Gen. Atomics v. Axis-Shield, 440 F. Supp. 2d 1083, 1095 (N.D. Cal. 2006). The relevant issue on appeal with respect to that term is whether the district court correctly concluded that a homocysteine conversion product must be derived from homocysteine. We agree with General Atomics and the district court that it does. 3 To determine the proper meaning of “homocysteine conversion products,” we need do little more than to look to the language of the claims. Here, the plain language of both independent claims supports the district court’s construction. The claims recite that the assessed analyte is “selected from the group consisting of the homocysteine conversion products of the enzymic conversion of homocysteine by said enzyme.” ’127 patent claim 1, ’717 patent claim 1 (emphases added). That language indicates that the “products” are those products that result from the conversion of homocysteine. Indeed, the latter portion of the claim limitation—“of the enzymic conversion of homocysteine by said enzyme”—emphasizes this point by focusing solely on homocysteine and its conversion into another compound or compounds. Contrary to Axis-Shield’s assertion, the language of the claim does not refer to just any product resulting from the homocysteine conversion reaction. Had the claim been written as “homocysteine conversion reaction products,” or “products of the 3 Axis-Shield does not argue that, under its HMTase infringement theory, the accused assay is within the ’127 patent claims because the analyte that is assessed is a homocysteine co-substrate. Therefore, our discussion with respect to Axis-Shield’s HMTase infringement theory is confined to the construction of the “homocysteine conversion product” limitation. 2007-1349 10 homocysteine conversion reaction,” Axis-Shield’s argument might be more tenable because that might suggest that the products may be any products resulting from a homocysteine conversion reaction. Indeed, when referencing the reaction as a whole in the specification, the patentee used broader terms such as “homocysteine conversion reaction” or “reaction.” See ’127 patent col.2 ll.42-45 (“The homocysteine co-substrate assessed in the method of the invention is a compound which reacts with homocysteine in the enzyme catalyzed . . . homocysteine conversion reaction.”) (emphasis added); id. at col.3 ll.1-4 (“[t]he preferred homocysteine converting enzyme used according to the invention is S-adenosyl-homocysteine hydrolase (SAH-hydrolase) which catalyses [sic] the homocysteine reaction”) (emphasis added). However, because the plain language of the claim refers specifically to the conversion of homocysteine when defining the group of “products” from which an analyte may be selected, the claim as written indicates that “products” refers to products that result from the enzymic conversion of homocysteine, not products that otherwise result from the reaction. Such a construction gives full meaning to every word of the entire claim term. Bicon, Inc. v. Straumann Co., 441 F.3d 945, 950 (Fed. Cir. 2006) (“claims are interpreted with an eye toward giving effect to all terms in the claim”). A homocysteine conversion product of the enzymic conversion of homocysteine is a product converted from homocysteine by an enzyme. For example, methionine is a homocysteine conversion product because it is simply homocysteine in which a hydrogen atom has been replaced by a methyl group. It is a modification of homocysteine. Thus, the district court’s construction, which requires the homocysteine conversion products to be derived from the homocysteine compound, is supported by the plain language of the claim. 2007-1349 11 In addition to the clear guidance provided by the claim language, we may also turn to the specification to determine whether the patentee attributed a different meaning to the term. As an initial matter, we note that aside from the Abstract, which mirrors the claim language, the term “homocysteine conversion products” does not appear in the specification. While the specification refers to other terms such as “conversion products” or “products,” those references, which do not relate to “homocysteine conversion products,” shed no light on the meaning of that claim term. The district court’s claim construction actually tracks the first embodiment disclosed in the specification. In describing the invention, the specification discloses the following homocysteine reaction which is catalyzed by the enzyme SAH-hydrolase: SAH‐hydrolase ’127 patent col.3 ll.1-9. According to the specification, SAH-hydrolase is the preferred homocysteine converting enzyme. The specification further discloses that the above reaction is reversible; that is, the reaction could run in either direction. In the forward direction, adenosine and homocysteine combine to form SAH. In the reverse reaction, SAH hydrolyzes to form adenosine and homocysteine. Id. at col.3 ll.10-20. This embodiment reflects the forward direction of the reaction. Adenosine acts as the homocysteine co-substrate, which the patent defines as “a compound which reacts with homocysteine in the enzyme catalysed [sic], e.g., a SAH-hydrolase catalysed [sic], homocysteine conversion reaction.” Id. at col.2 ll.42-45. SAH-hydrolase acts as the homocysteine converting enzyme. Both adenosine and homocysteine react in the presence of SAH-hydrolase to yield SAH—the homocysteine conversion product. 2007-1349 12 The specification teaches that “the amount of homocysteine in the sample can . . . be determined from the alteration in the adenosine concentration.” Id. at col.2 ll.44-45. Because SAH is derived from the homocysteine molecule and is the homocysteine conversion product, the district court’s construction of “homocysteine conversion products” reflects that embodiment. Axis-Shield asserts that the court’s claim construction is unduly narrow in light of other embodiments disclosed in the specification, including the second embodiment referred to as the inhibition embodiment. That embodiment “take[s] particular advantage of the fact that homocysteine acts as an inhibitor of SAH-hydrolase, suppressing the hydrolysis reaction which forms homocysteine and adenosine and pushing the reaction equilibrium in favour [sic] of SAH synthesis.” Id. at col.3 ll.16-20. In that embodiment, the level of homocysteine is measured by contacting the test sample with SAH and SAH-hydrolase. Id. at col.3 ll.48-55. As a result of the hydrolysis reaction, SAH would break apart to form homocysteine and adenosine. Id. Because of the inhibiting effect homocysteine has on SAH-hydrolase, however, “[a]ny homocysteine present in the test sample will counteract this net reaction, and thus inhibit the formation of adenosine, the amount of which is monitored.” Id. at col.3 ll.52-55. Thus, by measuring the amount of remaining adenosine, the level of homocysteine can be determined. Specifically, the amount of adenosine would be inversely proportional to the amount of sample homocysteine. Axis-Shield argues that the district court’s claim construction cannot be correct because it would not cover this inhibition embodiment. In particular, Axis-Shield notes that adenosine—which is the analyte being assessed—is neither a homocysteine conversion product because it is not derived from 2007-1349 13 homocysteine, nor a homocysteine co-substrate because it does not react with homocysteine in the homocysteine conversion reaction of the assay under the court’s construction. We are not persuaded by Axis-Shield’s argument. A claim need not cover all embodiments in a patent specification. PSN Ill., LLC v. Ivoclar Vivadent, Inc., No. 20071512, 2008 WL 1946550, at  (Fed. Cir. May 6, 2008). Prosecution strategies may evolve so that some embodiments are covered in a patent and others are not. Here, while it is correct that the inhibition embodiment is not covered by the asserted claims under the district court’s claim construction because the analyte that is assessed (adenosine) is neither a homocysteine conversion product nor a homocysteine cosubstrate, it appears from the record that that inhibition embodiment is covered by claim 17 of the ’581 patent resulting from the parent application of the patents in suit, which was originally asserted against General Atomics but subsequently dismissed from this case. 4 Thus, Axis-Shield’s assertion that “homocysteine conversion products” must be 4 Claim 17 of the ’581 patent reads as follows: An immunological method for indirectly assaying homocysteine in a sample, said method comprising the steps of: (a) contacting said sample with S-adenosyl homocysteine hydrolase enzyme and S-adenosyl homocysteine wherein said S-adenosyl homocysteine hydrolase converts said S-adenosyl-homocysteine into a non-labelled analyte wherein said non-labelled analyte is adenosine; and (b) determining the presence or amount of the non-labelled analyte without chromatographic separation by contacting said sample with an antibody which specifically binds with said non-labelled analyte and with a detectable hapten for said antibody other than said non-labelled analyte and wherein determining the presence or amount of said non-labelled analyte is effected indirectly by determining the presence or amount of said detectable hapten either bound or not bound to said antibody, 2007-1349 14 construed broadly so that the asserted claims cover the inhibition embodiment is inapt, particularly in light of the plain language of the claim, which is both clear and unambiguous, see Ethicon Endo-Surgery, Inc. v. U.S. Surgical Corp., 93 F.3d 1572, 1579 (Fed. Cir. 1996) (rejecting a proffered construction because “the plain meaning of the claim [would] not bear [such] a reading”), and the coverage of this embodiment in the parent patent. The patentee chose to use the term “homocysteine conversion products” in the asserted claims of the ’127 and ’717 patents, which require that the products at issue are those that result from the conversion of homocysteine. As such, we decline to depart from the plain meaning of the claim term by expanding the scope of “products” to include any product resulting from the homocysteine conversion reaction. Accordingly, because the analyte assessed in the accused assay is SAH, which is a conversion product of SAM, not of homocysteine, we conclude that the court properly granted summary judgment of noninfringement based on Axis-Shields’ HMTase infringement theory. B. Axis-Shield’s SAH-Hydrolase Infringement Theory The district court also granted summary judgment based on Axis-Shield’s SAHhydrolase infringement theory, in which Axis-Shield appears to assert that the accused assay infringes the asserted claims because it allegedly uses a homocysteine conversion enzyme, viz., SAH-hydrolase, and assesses an analyte that is either a homocysteine co-substrate (adenosine) or a homocysteine conversion product (SAH), wherein the amount of the non-labelled analyte is indirectly proportional to the amount of homocysteine in said sample. ’581 patent claim 17 (emphases added). 2007-1349 15 during the latter phase of the process. The district court rejected Axis-Shield’s assertion. In a well-reasoned opinion, the court determined that the accused assay fails to meet the properly-construed claim limitations because it cannot differentiate between SAH produced from a SAH-hydrolase reaction and that from an HMTase reaction. It therefore does not meet the “assessing a non-labelled analyte” limitation. In challenging the court’s decision, Axis-Shield raises several arguments in asserting that the accused product infringes under this alternate theory. Axis-Shield relies in part on its previous argument that the court erred in construing the term “homocysteine conversion products.” For the reasons stated above, that argument is rejected. Axis-Shield further argues that the court erred by improperly construing the terms “homocysteine converting enzyme” and “homocysteine co-substrate,” and also erred by failing to correctly apply other constructions stipulated by the parties. Having carefully reviewed Axis-Shield’s arguments, we find no error in the court’s analysis and conclude that Axis-Shield fails to identify any basis for reversing the court’s decision. Accordingly, we thus affirm the court’s grant of summary judgment based on AxisShield’s alternate theory. We have considered all of the remaining arguments Axis-Shield has raised in its briefs with regard to its theories of infringement and find them unpersuasive. 2007-1349 16