3 ATP&;s are formed in the following steps of Kreb&;s cycle

3rd Step: Formation of Alpha-Ketoglutarate i. This reaction is a two-step process, both catalyzed by the same enzyme, isocitrate dehydrogenase (Step 3, Fig.18.2). In the first pa of the reaction, isocitrate is dehydrogenated to form oxalosuccinate. It is an unstable compound which undergoes spontaneous decarboxylation to form alpha-ketoglutarate. ii. The NADH generated in this step is later oxidized in electron transpo chain (ETC) to generate 3 ATPs. iii. Isocitrate (6 carbons) undergoes oxidative decarboxylation to form alpha-ketoglutarate (5 carbons). In this reaction, one molecule of CO2 is liberated. iv. The isocitrate dehydrogenase has isoenzymes; the mitochondrial form utilizes NAD+, while cytoplasmic enzyme is NADP+ dependent.Ref: MN Chatterjea Textbook of Medical Biochemistry, 6th edition, page no: 218