lactate dehydrogenase activity assaylactate dehydrogenase assay protocollactate dehydrogenase release assaylactate dehydrogenase enzyme assaylactate dehydrogenase assay kitlactate assay sigmalactate dehydrogenase releasepyruvate kinase lactate dehydrogenaselactate dehydrogenase kitldh assayldh enzyme assayassay development